I have tried both the hobbico and Tower tachometers... both seemed to work fairly well. I have no reservations recommending either. I have not tried the H9 version shown above, but no doubt that works well too.

If you consider a tach is more of a reference than an absolute measuring device, they are just fine for the typical modeler who wants to compair performance between props or as a setup varies day to day.

I have an expensive Allen Booth tach, but honestly for most of my racing and sport needs I still use a 20 year old Royal $25 tachometer. Similar to the hobbico in size and performance. Most of the time I just lay it on the ground next to the nose of the aircraft, placed aft of the prop, and it reads rpm quite well while leaving both of my hands free. My test stand includes a simple (rubber band) tachometer mount just after of the engine for the same purpose - so I do not have to hold it the whole time.

The Hobbico tach seems to do just as well with the hands-off approach, as long as the sensor end is propped up a bit off of the ground.