Given that it hasn't sold for weeks on Ebay, then you post it here and suddenly it's sold, I'm guessing it's a member/lurker on here that bought it. Wasn't me!
If you are just wanting a Tach, Yes there's lots of better and easier options. I just use a tiny-tach that's actually designed to be mounted to a machine as an hour meter and tach. Works great for me though. The mower monitor was probably used very little even by dealer mechanics, but I'm sure was something "required" by lawn boy to have to be sure that the flywheel brake was working properly and stopping the engine/blade within the ANSI required limits. 99% of people don't care, lol. I have a couple '80s models I replaced the brake spring with a lighter weight spring because of the amount of tension required on the flywheel brake cable was really high and I was afraid of the cables snapping, which costs around $50 to replace, no thanks!