How would i know? Well...i sell them. I own a 70cc Pitbull too. I am a seller for Hooper Imports (google it). I picked the pitbull and trail rider because they are copys of something that parts would be no problem getting. I will be totally honest here. The quality isnt honda , yet. what you do get is a good start especially if you plan on using and abusing your machine. The old Hondas are starting to be collected by boomers too so.....If you would want either one of these in a honda youd be paying at least twice to three times as much if you want a really nice example. If there is anybody that wants any motorcycle or scooter Hooper Imports sells and lives around central minnesota (or willing to drive) i will sell it completely assembled with a 6 month parts and labor warrantee for the same price. Long Beach Cycle, Glenwood MN 56334. 320-634-3022. Im a stay at home dad so call at anytime.

Now the showdown.

The 70cc Pitbull is a vast improvement over a Z50 in the power department. In my humble opinion a four stroke 50cc is dangerous on the street. The get up and go just isnt there. The pitbull also has an electric start....very nice. For tough trail riding the pitbull is great. The height and width is an advantage. Fewer branches in the face is good. Would be perfect transportation on a deer path. It has a super low first gear and can crawl up a very steep hill. It will climb as long as there is traction and forward weight distribution. Im 5'10" 165 lbs. I fit great. plenty of room to move, surprisingly. They have a big, if kinda ugly seat that is more comfortable than most large street bikes ive owned. The brakes, for drums, are pretty good. Hard to be great in this department for me since ive owned a few sportbikes with BRAKES! The handling is quick on the street and good on the open road. (40-45 mph comfotably. 50+ in full tuck.) Just keep you hands on both grips when your going good. No waving at pretty girls. The spedo is in mph and the odometer is in kilometers. Why? Dont know. Mileage is around 120 mpg in adverage driving. In sustained speeds on the highway i would think it would get around 150 mpg. You will have to convert kpg to mpg. Take your kgp and multiply it by .64 to get mph.
Improvements: Hooper Imports sells a honda like headlight bucket that is red (not chrome), shorter than the pitbull bucket, and with only one idiot light hole.  Very honda looking and big improvement. Ask for it specificly! Dont mess with sprockets. They are about pefect. Bigger engines are a great improvement to up to a 110cc auto clutch is straight  forward with only minor changes to the exhaust. (I expain on this forum how to put a big engine in a pitbull. Do a search if your interested). I have an ebay bought front end on mine. $365! it came with the forks, tripple clamp, top clamp, front disk, caliper, master cylinder, brake line berings and races. Eazy to instal. I did it mostly for the cool factor. I also mounted a set of original honda fenders. The fenders are a great look. BIG improvement.

The 110cc Trail Rider. Ive had an eazier time selling these do to the engine size and being a little taller. The 110cc electric start is better than the hondas 70cc engine as far as power goes. My opinion is that they handle a little goofy on the street. they fall going into sharp corners (not to the ground). for riding on a trail they are fine. The speedo like the Pitbull is in mph and the odometer is in kilometers too.  Ive had problems with the pressed rims having unacceptable (to me) runout to the point of me having to take them apart and clock the rims to make the rims wobble a little rather than bounce. Every one ive sold has had this problem to some degree. (the pitbulls rims are perfect) I told Larry from Hooper Imports and he half didnt belive me or thought i was exagerating. He said that he never had any complaints before. Maybe my customers and I expect better? there is a fix though...buy a set of used honda rims on ebay. The brakes work fine considering that they are the same brakes that are on a Pitbull. The trail rider is not really pretty in my opinion. It wasnt pretty as a honda either. The only advantages it has over the pitbull is like i said in the begining; height and engine size. 
Improvements: Honda rims if yours arent true. Honda fenders are much better quality. lock tight nuts and bolts on this one. Its not a bad motorcycle for the money. If you dont mind commiting a sin you can pull off the ugly graphics that come with the bike an put on honda stickers or leave it plain.

Verdict. the Pitbull unless you just dont fit on one. You can go on a diet if your fat but i dont recommend cutting your legs off at the knee if your too tall.

If i were Lifan......
I would start with a Pitbull. Drop a 110cc, 125cc or 138cc hand clutch electric start engine. Put on a shorter painted (not chrome) headlight bucket with only one quality looking idiot light (neutral light). The stock idiot lights look crappy. get rid of the annoying blinker beeper. QUALITY steel fenders. They wouldnt have be chromed. Get rid of the silly graphic on the side of the tank that are clear coated over (grrrrrr). Regular fork front with front hydraulic disk break (which they apparently already make). Find a better looking (Stanley style) tail light.
Options: Two paint options; red or in primer. Street tires. Aluminum rim halves. billet Engine dress up trinkets, etc.
I would spend more money in the fit and finish department and sell the motorcycle for around $1600.

Ive got a panda funrider. its basicly the exact same thing as a pit bull.
there are alot of good points about these little "motorized bicycles"
thats how the 50cc is listed on the MSO so there are benefits.
if you can stand the lack of power (the 70cc version is probably a bit better and it has electric start) and can drive it as you were driving a bicycle (30 mph all out tops). you can get 150+ mpg all day long. i put a lifan 138cc oil cooled (converted to air cooled) engine in mine bought off Ebay. now it gets an awefull 125 or so mpg. the engine transformed the little guy into a great town bike. i put an 18 tooth counter sprocket on the engine to be able to make some use of first gear (still way too low for the street but about right for deer trails). i bought a pipe for a mini mx and chopped it down so the muffler fits where the original was. the end is aimed at my right rear shock and since its still running a tad rich is making my rear fender black with soot. oh well. the lighting is tons better too since there is a more powerfull alternator on the 138.
it is a ton of fun. wheelies are eazy. no yanking on the bars. just click into second and snap the throttle open a bit. third gear too with a bit more throttle. the brakes are fair, a bit woody but im used to sportbikes so...cornering is awesome. the tires are very soft and grippy although i have gotten the rear to step out on a dirty corner. the cops rubberneck (well they used to) to look for a plate, which it has. i can drive this where 4x4 wheelers cant fit and i can get there legaly on any road.  i plan on studing out a set of tires so i can take it ice fishing too. it would be great for getting to a tree stand too. not as obvious as a four wheeler on narrow trails.  if you want to save a bit on gas and live just a few miles form work id recomend this setup.  i have around  $1200 into it. if you buy a pit bull, engine, pipe, aircleaner, clutch cable and clutch lever at the same time a dealer should cut you a deal. the wiring is a simple 6 wire. three colored wires match right off and the other three can be figured out just by taking off the left engine cover. I tossed the battery from mine too. less to replace and works fine without one. if you figure in $3 to possibly $4 a gallon gas in the not so distant future the bike would pay for its self pretty quick. especially if you drive a vehicle that gets under 25mpg. do the math. no. really. do the math.

PS if your of the large of size- lifan sells a trail 110 that is a copy of the honda trail 70/90. it is a bit taller and more room.

hi
i had a 00 jincheng panda sitting around and not being used much except to give the kids a ride around the yard. then i got a wild hair and bought a 138cc lifan engine from ebay. to be honest it was a shot in the dark. i didnt know how it would work. i bought a xr dirt bike pipe when i bought the engine too because i was pretty sure the stock one would never fit (it will with modification). i got the engine and in about 2 hours of wrenching and wiring was riding it around. lots of power and much more fun. i turned in my mso and got licence the next day and started drivng it to work. it seemed like the perfect commuter/town bike. then it happened.....bad sounds with just enough power to keep it running......a friend with a truck brought me home. then i started to disassemble. my first thought was a ring broke and was causing drag and making the squeeking noise. took the head off, then the cylinder. to my surprise it looked great. piston was like new. cylinder looked freshly honed. i slowly turned the crank while holding the rod to feel for bad bearings. fine. then i looked at the head. dry. not good. the cam was scored and the rockers were bluing from heat and wearing into the lobes. no oil was getting to the head. now i knew there was oil in the engine so i thought the pump wasnt woking. nope. it turned out that upon assembly the oil galley to the head was mostly plugged by the o ring between the head and cylinder. a 5 cent part. i got ahold of the sales person i bought it from. first he offered to replace the head so i sent it in. he claimed he couldnt see any dammage. i dont think he knew what he was looking at but he offered to replace the whole engine. done. now this story doesnt seem like a glowing endorsement for lifan engines but remember this engine went almost 100 miles with next to no oil getting to the head. the o ring was, a stupid, yes, simple mistake. being able to see the quality of the internal parts impressed me enough to check into becoming a dealer myself.  if anybody wants to make their z50 a real motorcycle that isnt dangerous to drive in town from lack of power to get out of peoples way, find a good dealer and do it.  i is again a great town bike.
  to make first gear usable i bought a bigger counter sprocket. a 17t. if i find a 18t ill try it. top speed id say is least 50 mph. i weigh 160+. if i used a 110 engine with an auto cluch i think the stock pipe would work with minor mods (different pipe to frame mount and larger diameter exhaust tip)save some money and be quieter (a sleeper). if anybody wants to know which wires from the engine go to which wires from the harness on a jincheng panda, just ask.
with the orignal 50cc engine i drove 111 miles on .7 gallons of gas. the 138cc lifan still gets a little over 100mpg. they are fun, fast (in town), green, inexpensive, honda designed, eazy to work on, take up less space than a bicycle in the garage (or living room) and a great way of meeting people, if you find a good dealer that is.
later.