StephenH

I've used a couple of the cheap Schwinn ones, available at Target or maybe Wallyworld.

They have a magnet that clips to your spoke, so no resistance from little wheels or anything. When you first get one, you need to calibrate it to your wheel size. Roll your wheel one revolution with load on it, measure how far that is, convert to millimeters, and enter that in the computer.

Biggest drawback is that they lose all their settings (including total accumulated milage and calibration number) when the battery goes dead, which was like after 6 months for me. New battery was $5 at Radio Shack. So unlike a car odometer, you can't tell how many miles on the bike.

I really like having one. It helps to keep my speed constant, so I don't pass someone and then slow down in front of them. Helps to improve my speed. Helps to know how far I've gone, how far I have to go. I don't use the time function.

They are fiddly, like a digital watch, where you have to press this button and then that button, etc., while reading microscopic directions.

I accidentally bought the cordless version and discovered the sending unit wouldn't fit between my fork and my spokes. No problem with the normal version.

I've not used the more expensive computers, so can't comment on them.