Do it, I did, more hp, more torque, thats what i noticed most, smoother torque curve...but do the breather mods, exhaust and or de cats etc etc.
Funnily enough, mine gained hp after adding the mods without remap, then with uprev pushed it just over 300bhp. Not bad for a DE.
Also gives you a good idea as to how healthy your engine is too.
Horsham Developments were great.