There are a couple of different.....ah...classes of the chinese stuff. Some are good some are not.
Find out what "brand" they sell and do some internet checking.
If you are going to use one as a pit bike I would say I doubt that you would have any trouble with it, loctite every bolt you can find. The plastic is very brittle.
I bought my kid a chinese dirt bike and the thing has been fantastic he has beat the crap out of it and it still is going strong, and it is crazy fast....too fast, but kids will be kids and dads will be dads.
I hope the following is ok to post here:
Check out the
www.thumpertalk.com and look in the Dualsport section of the threads, mostly doing with bikes but you can get an idea of who to steer clear from, as well as a ton of links.
I am thinking of getting one myself, just on the experence of the bike that I got my kid, perfect pit bike, even the small ones have e-start.