I'm late to this discussion... But I have the Cateye double wireless computer (the cadence model) and I really like it. It's been super reliable and accurate for me. The speed/cadence sensor is designed to be mounted on the chainstay (speed magnet is rear-wheel mounted), and I have not had interference or signal-dropping problems at all.

My bf, after a month of agonizing over which computer to get (I think we looked at each and every computer at all 3 local bike shops plus all of the computers at Performance and Nashbar about 5 times... needless to say I was to the point of "it doesn't really matter that much, just make a choice) -- got the same Cateye, and has had similar good luck with it.

As for zip ties -- I keep a few sizes in my bike tool bag at all times. They're useful for all sorts of things.