The Cateye Velo 7 speedometer is the basic wired model. The Velo 9 adds calories and CO2 - not needed IMO. The Urban Wireless model eliminates the wire without going bigger and bulkier, but you have to wake it from sleep mode, or it won't record your ride. The wired models wake automatically, but do not zero-out without holding the button. Either are more accurate than a phone GPS, provided you set the size of the wheel accurately in the setup routine.