I went with a slightly different approach to the computer. I also don’t care about cadence and have never been a fan of adding wires or magnets. I certainly have never been a fan of calibrating checking against another biker’s computer and then re-calibrating!!!
I had the advantage of already owning a Garmin eTrex GPS (Retail about $109.00) that I also use for navigation while fishing. Garmin makes a handy dandy mount for bikes. I get 18 plus hours out of 2 AA batteries. EXACT measurement of mileage and speed. Granted a little bit more money but my ex girlfriend said I could rationalize any dollar amount for my bike.
Remember, wants are far more important than needs.