I use a pretty simple Sigma Sport wired computer on both my road and mountain bikes. They are a 90's era computer and I still can get them new off ebay for $15 or so.

I no longer ride by the numbers, but it is nice to check on mileage, especially for those times when I have only gone a few miles and have no motivation. It kinda gets my butt into gear. And yes I've crashed and have not lost it.

John