I have a "cheapie" from Tower that I found for $12 on one of their bargan sales. I use it quite a bit.

http://www3.towerhobbies.com/cgi-bin...&I=LXPT31&P=ML

One of those things I never thought I needed until I tried one. Hasn't changed much in my flying, but it sure simplifies finding a good top-end starting point. I wind up the engine and set the high end to maximum rpm and then back down 400 rpm. Also a help when choosing the right prop for a given engine & plane. It still depends on flight testing but it is never bad to have additional useful information.