Update on TinyTach
Well I went ahead and purchased a TinyTach diesel. The installation was a snap, my only concern was having a long enough cable to go from the transducer to the module. It is a coaxial cable, and so it would not be easy to correctly splice on an extension.
I purchased the unit with 12' cable (default is 8') and had no problems installing the transducer & running the cable neatly from the engine to the yanmar cockpit engine console panel. I mounted it just under it.
It works fine. I especially like the true engine hour meter which is built into this unit.