I have a tach and do use it. Saito tells you to keep it under, I think, 4000 rpm for the first 10 minutes or so of running. The tach helped me do that. Even with recommended props the engines don't always turn the way they're advertised, high or low. I use the tach to make sure my YS's are in the right ballpark, on the ground, when changing props. Maybe y'all are better than me in sensing RPM. I don't use a tach all the time, but do use it occasionally, and need it when I use it.