They also do a full titanium backbox for about £150 or something, thats the only thing in the Rage range that remotely appeals to me. Otherwise theyre far too Nova-ey - the new Peco, but without the vehicle-specific fitment!!! And the backboxes are tiny, so if you dont fit a full system with a freer-flowing centre section then Id imagine youre likely to lose a lot of low end power/torque from the loss of back pressure.
On a positive note, they sound very loud.