I have a zzp one, i like it.

get the 2.5" bolt in (it will be easier to install) going 3" is pointless since its going right into your stock cat-back. Going cat-less is up to you, it will smell like gas if you go that route. You will need upper and lower DP gaskets, installation is easy (4 bolts) just use plenty of WD-40 because they will be rusted.