Wireless bike computers come in 3 varieties, analog, digital, and GPS based.

0) Wired. Cheap and reliable. Basic.
1) Analog. Usually cheaper, very prone to interference and drop-out. Not worth the money.
2) Digital wireless. Not cheap (~$75), not super functional, less prone to interference. Too expensive for what you get. Spend a little more and get a GPS.
3) GPS. Not cheap (~$125+). Easily transferred between bikes. Tons of functionality. Usable for Strava and more advanced ride tracking. Better monitors can handle heart rate and power meters.