I know the bikes been around for a good few years and am wondering what the differences are.

The major change I've noticed is in the K models where the front and rear have changed. But they all seem the same externall from K1 - K3. K4 has changed a bit.

Is there a particular sought after model? or one to avoid?

 

uy a k5 these are quite c heap new if you want a red 1 ir buy a used blue n white one or a 750