Yeah, that is a solid spool in the bag, you can achieve the same effect by filling your rear diff with blu-tac(poster tape) as you put the cogs in.

A front one way is used by a couple of the boys at D1RC, others use it for a tighter track, it creates a handbrake style effect so if you come of the throttle as you enter the turn it will swing the rear round, some swear by it, others dont, I got an 03f and its so good it really doesn't need one tight track or not.