Do you mean a servo? Depends how you ride it and what you would personally prefer All it does is adjust the powerband to the rev range your at so instead of a massive hit it will be smooth all through the rev range..
I prefer the servo. Although it's not set up right ATM. However I've just found out how to put it back to standard so I will be doing that as soon as the gearbox is back together.
The bike should be quicker with the powervalve and servo installed and adjusted according to the book , that way you get power all through the rev range . Pinning the valve open only makes it feel quicker because of the lag .
I buy parts when I want to do a mod and mod that in stead that way if it dont work I can still ride my bike. I have kept all my spairs and can return my bike back to std. If I ever sell it.