I would like to add a bit of text to my earlier post.
I mentioned that I have a couple of nephews that own Mongoose bikes and have had no problem with them. This is true, the youngest is 14. About a year ago he got interested in cycling, mostly because he knew I did it and he went to a race or two and watched me. I borrowed a bike from a friend and took him riding a few times to see if it was going to be "his" thing or not. He fell in love with it and wanted to do more. His dad bought him a X-store Mongoose (after having me go look at it) and he started riding...everywhere! It didn't take long before he wanted to try off road trails so I took him a few times for some mild off roading. He was still very interested and excited about it. He rode that bike several hundred miles last year on and off road. This year he wants to try racing. Currently we are building him a VERY nicely spec'd GT i-drive complete with discs and air suspension.
The moral of this story...if you are not sure you will take to cycling, or are on a tight budget, buy what you can take care of it and ride it. If you like it you can always upgrade to a better steed and continue enjoying cycling. I would never tell him or anyone to "race" an X-mart bike, but riding one is not generally a problem. The advice I have seen here on this I agree with mostly, especially the parts about having the bike checked out for proper assembly. What I don't agree with is the "don't buy one for any reason" attitudes. That type on opinion
may just keep a potential rider out of the sport.
Please no one take any of this personally, once again just my opinion.