I put an old Trek cyclo computer on my Schwinn Spin bike. I just put a rare earth magnet right on the outside of the flywheel and it has never moved. It also has a cadence sensor and gets the job done. I also have an Edge500 and use that to track my HR. I do have enough bits to put a Garmin cadence sensor on the spin bike and with the HR strap, would be nice to have to record some data from the spin bike sessions. Maybe that will be a good Christmas day project.

Good luck!