from my experiance (only 6 months) with my polar forget about the "ownzone" functions. you just need to figure out what your MHR is for cycling (and other acticvities if interested).
as mentioned above do the 2x20 if you can (something i have yet to do!!!) to figure this out. personally I guaged mine from the age formula then attended a few spin classes and after reaching my age formula max on a couple of occaisions (when i was about to black out) concluded that for me my age formula max was pretty spot on (not always the case for everyone)
mine MHR (192, set mnanually in my polar) probably isn't spot on but i don't race and it serves as a useful benchmark for some rough zone training. I found the biggest thing it taught me was riding what felt at first to be painfully slowly during recovery/endurance rides. 3 centuries later, i conclude the polar has haelped me no end! good luck