If you want a Heart Rate monitor that connects to either MC and/or a TCD (if you have one) then you need a device that broadcasts over Bluetooth. As far as I can see reading various threads it seems that it’s not possible to connect an Apple Watch for this purpose (there is a long thread about this on this very forum). I can confirm from personal experience that the Garmin Dual HRM connects and has the added benefit that if you use a Garmin head unit it will also connect to this over Ant+ as it broadcasts using BT and Ant+. The HRM is a chest strap so perhaps not as convenient as a watch but that depends on what you really want. Hope this helps.