Eh,
they're ok. If it's cheap, I'd say go for it. The biggest drawback is you're getting a carb'd bike. It's based on the 98-02 ZX6R, so it's a ten year old design, which makes it heavy by 600 standards. My recommendation? Find an '03 or newer ZX6R, '01 or newer GSX-R600 (this is what I have), '01/'02 F4i '03 or newer 600RR, or an '03 or newer R6 or R6S. All of those are Fuel Injected (and actually, the '96 and up GSXR750 is FI too) and would be worth the difference.