I only have a little boat, and have no engine instruments on the console. I needed a tacho so I can safely get the most outta my outboard.
I liked the look of the Tinytach series (being sealed, self-powered, digital tachometer with resettable hours counter.)
Emailed Tinytach in USA, and next day their UK agent replied. He was ever so helpful, identified the tach I needed and sent one in the post, "make sure it works on your boat, and we will square up later" - excellent!
The standard cable was too short to mount the counter on the console, he told me how to extend it.
Fitted tach at weekend - absolute doddle - works great!
if you are interested, the chap's name is Richard Dunn, and his email is firstname.lastname@example.org