Well the kind of testing that is done on these phones are far from truly legit manufacturers.. Legit manufacturers spend a heck lot of time abusing these phones to make sure they don't fall apart after a few months use.
Knockoffs "usually"(when it comes to phones) are made with crappy material(this I know firsthand) and the radiation levels far surpass what the FCC "allow" from what I've heard. Other than that.. if your phone breaks for some reason, you're usually left without a warranty or any signs of customer service at all. Oh yeah also the exploding batteries..
Link to
NYT here, but parts of it seems one sided so I don't know whether the high radiation part is really true, or if the batteries really have a higher chance of exploding just because they are fakes.
For fun, I'd probably get one. As my main phone? I would really rather not deal with the hassle.
My .02