ORIGINAL: Charlie P.
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.
I use that one as well, it works great for my needs, since I run primarally 4strokes its a handy tool for the first tune of the day, I always start up on the rich side lean to max rpm and back it off 4-500 RPM the tone difference is imperceptable at full throttle the tach takes the guess work out of the loop,for me at least when I notice a tone difference and check with the tach its at least a 1,000 RPM change from peak for a 4 stroke that a big drop in power.
when tuning the few 2strokes I have the pinch test is all you need for a smooth running tune.