You can use HR zones when not on your trainer. If you have a power based plan then you will need to set your 80/20 HR zones on your device so you can keep to the appropriate intensity.
Our 80/20 subscription membership gets you access to the full workout library – so in your case when you are riding outside you could just replace the power workout with a HR workout. Something to consider if you think you will be switching around a lot and not looking to get a power meter anytime soon.
Subscriptions