I have one of the digital units. They are pretty accurate, but eventually leak oil into the display. They aren't hard to disassemble & clean up, but it takes a few minutes.

You really don't need an oil temp. guage, but it's handy to have. Harley has cooling down pretty good unless you have modified your ride. If you're makin' changes to your bike I'd recommend a fairing mounted oil temp. gauge in your fairing. Easy to do, & well worth the investment.