I spin in the winters because the roads are awful where I am. The Keiser M3s are a good spin bike, but calibration will vary between units in the same gym. If you are going to train, be sure to use the exact same bike whenever possible, as that's the only way to gauge progress. The useful metrics *on a relative basis* are watts, kcalories, and rpms (cadence). Distance is useless.

Do NOT try to compare watts on an M3 to watts on a real bike. I can hold 300W on many Keiser M3s for a 60 minute class, but am a lousy cyclist. On a real bike for the same amount of time, I estimate my power to be about 230W.