I have one very similar to this
The actual one I bought may not be made any longer. I mounted it to the cross bar. It reads the rpm about once every .5 seconds. I bought it on sale but you probably can find similar ones on ebay for less money. For the low cost and ease of installation I rate it pretty high. I didn't think I would like or use the hour function but I do like it. BTW, they are $30 each but if you buy 10 of them they are only $18 each. Do you have 9 friends that might be interested in one or more?
This is the one I have. 99 hours in the saddle when I took this picture. My next picture will be at 168 hours. That will be equal to one week solid -- 24/7 -- of the engine running and me riding.
I hope this helps. Tony