I can't imagine tuning a four-stroke without a tach. My ears are simply not good enough to do that. I can't hear a 300-400RPM change at between 8,500 and 10,000RPM. I use an inexpensive $20 tach that does what I need it to do. Nothing fancy.

At the same time, I can't imagine tuning a two-stroke with a tach. Totally unnecessary.