I can't help you with the 600, but I absolutely LOVED the TNT300 I rode. It was ergonomically perfect. Big enough for my fat ass American-sized body, the controls were all in the right place, and it just fit me like no other bike I've sat on in a very, very long time. I took it for a half hour test ride and it was really, really good. I liked it so much, I was prepared to buy one (Just not that one, I wanted the white color). But then rumors of the Leoncino coming out in the USA started, and I decided to sit on my hands. It was hard, because in the interim the 302S was released. Same TNT300 looks, but 18cc larger motor, 5 more horsepower, and wider sportbike rims all for 4 pounds extra weight sounded like perfection. But I held off... and two days ago put a deposit down on a Leoncino Trail, in red.
I guess what I'm saying is, I don't think you can really go wrong. These bikes have been out some time now and are pretty reliable. I say if it tickles your fancy, go for it.
Charles.