They give a much better response with boost and chances are your current actuator will be past its best anyway. It's a manifold off job to fit them so budget a few hours and some new gaskets etc. Measure your current actuator and set the length the same as that for the first run, disconnect the N75 plug and see how much boost you get. Around 8psi will be fine. You can add more preload (shorten the rod) if needed but don't go crazy or you'll have major problems
Don't replace your N75 unless it's knackered, I'm still running a C version that's about 12 years old and it's fine.
If you go with a K&N make sure it's not oiled otherwise it will shorten the life of your MAF