I really like running my TR workouts via my Garmin 830.
ERG mode works fine and I like that it records all my cycling dynamics data without having to dual record.
The only issue I’ve run into is that the allowed power range in the recovery intervals are sometimes stated as “below x” rather than “between x and y” for example if a recovery interval should be 130w on the Garmin it will say stay between 1 and 130w but ERG mode translates this to a value of 65w - which is far too low obviously.
Doesn’t seem to affect all workouts though.