Decat makes it rev a little free er apparently, can't say as I noticed much difference tbh, 2 reasons I run decat are 1 - my Renault cat won't deteriorate and rust as fast sat in my cupboard so I won't have to buy another when I need it, and 2 , i like it loud lol, but it does get annoying at times.
rs tuner is ok, seems to smooth the torque out.