Jon B.wrote a review of PowerTap P1 Power Meter Pedals on February 4, 2016
Familiarity: I returned this product before using it
I just called Garmin to confirm, their latest firmware on 920xt and Fenix 3 have wiped out the ability to change your crank length, which means unless you have 172.5 cranks, the power reading will not be accurate. As many riders use Garmin head units, this makes the pedal based system a no go. Hopefully Garmin will release an update to give the ability back, but on the phone they gave no indication of it.