PhilPub, likely the hr strap wasn't working properly.. Hasn't even registered if showing 1.0. Same on all you have recorded?
I had a Suunto watch, 3-4 years ago, the feature works really well there since it gives you a diary/ program of what it recommends based on the sessions you've done, a mix of 1-5 sessions over the week.
The garmin TE on 610/910 doesn't do this. It just gives you a number, can be shown on the screen changing as you exercise or just shown later in the stats. No advice offered.
I've done races with my Garmin, they're usually a 5 if a race effort regardless of length.. Tempo run came out a low 4. shorter speed session a 3.8, 2 different gym circuits, one with longer cardio periods less recovery 4.1, the other 3.2.
The feature does work. Just depends how you use it, or take its advice.