I had used relatively expensive wired Cateye and sigma computers with cadence sensor. they all have similar problems:
- the magnet needs to be very close to the receiver. I had to build up quite a contraption on the chainstay or the fork to get the receiver close enough (wasn't possible with the included material). that magnet that gets attached to the spokes is just too small. Occasionally the magnet turns and needs to be re-adjusted.
- the cadence magnet slips on the crank with the included rubber. one even fell off. i ended up buying a large molybdenum magnet and glued it on the crank with epoxy.
- every once a while one of the signals (cadence or speed) doesn't display because the computer needs to be re-reinserted in the base.
- One of my bikes lost the cadence, sensor must have failed

So, wired and expensive brand also doesn't give you painless computers.

The newer BT/ANT cadence are much better and don't need a magnet, they just use an accelerometer. IMHO speed can just be derived from GPS. Yes in deep canyons this may be spotty. But an rpm-based speed has its own problems. You need to measure the wheel circumference exactly and account for pressure and tire-sag. Wheel swaps and sue on different bikes makes an even better case for GPS-derived speed.

If speed is all you need, there are $50 GPS speed computers. No fuss with wheel sensor etc.