I know that the ramp plates (the treats rumpus for that matter) are different. Ive done testing on all 4 with the same weights, etc and there is a discernible difference.
Anyway, i only have the derbi stock 6 roller to compare atm but is there a difference in performance between the 3? Derbi 6 has the holes for the grease shield and groove for the gasket.
I read that the TJT allows the belt to sit lower so theoretically quicker take off (from the derestricting flat reed thread):