Neuspeed exhaust experiences?

I've got a Neuspeed exhaust, comptech intake, and neuspeed springs on the way for the S2K.

Unfortunatly, after reading a few reviews about it people were complaining about the loss of power... Anybody have this experience?

One of the people who was complaining about it said they had bolted it on themselves... Seems pretty straight forward, but could he have done something wrong?

Thanks for the input.

Ray