I just broke / smashed a 10 - 20 year old Hobbico tach that might have cost $20 way back then and replaced it with the same thing. It can give obvious junk readings but if you know roughly what you ought to be getting, you will disregard the 50,000 read out and wait until it settles down to what obviously looks feasible. The reading will fluctuate in the hundreds column once it is reading like it should. I can't see needing anything more expensive than this.