i honestly would rather buy Tein's over k-sports. I've heard tons of horror stories about the quality of ksports since buying mine. as far as i know no one on here has had any problems with them but most of us don't push them so that could be why we haven't had any issues.
personally i'd try to stay away from FF and Ksports, anything made in china is usually a questionable investment unless the price is right and you accept the risk that the quality may not be comparable to more reputable brands.
what have you heard john? i havent heard anything, and everyone on here seems to be satisfied with their f2's and ksport's...including me.