@ Longjog, unfortunately he lives in California
@ Foo fighter
Garmin bike mount does not seem compatible as the slots are narrower on GB devices.
GB580P, GB580F (not GB580B) are compatible with ant+ HR, speed, cadence and Power Meters.
I don't own and use this accessories but it is in the menu of GB580P although not in the user manual (only in quick start guide).
Probably because it was copy from first beta firmware.
It should be added in the user Manual:
Sensors-> HR, Speed, Cadence, Speed/Cadence combo, Power Meters
Sorry for the delay answering that question
I deleted some posts because there were pointless since now the answer is obvious. I do not want to mislead anyone.