Apart from the one I posted (and remember there are about 50 different vendors selling the same item) I've only used a stroboscope on mower engines. The stroboscope is not convenient unless the engine has a visible flywheel, and even then is not as easy to use, mainly with regard to safety, and reliable accuracy.
If you are looking at tachometers similar to the one I posted, please remember two points. First, there are several vendors selling a variant on that design which simply has a slot in the back which the pickup wire is run through, rather than it being hard-wired to the tacho module. They are a couple of dollars cheaper. I haven't used one of those so I can't give an opinion on how well they work. The second point is that old versions of the one shown in the link I provided, like mine, have the battery embedded in the module's potting mix so it can't be replaced. At least some new versions of that tacho now have replaceable battery. I think that would be a positive feature if you use the tachometer a lot.
