I don't think they have a functional prototype, so probably difficult to predict a qualitative comparison to other types of motion. Honestly my guess is that it

I don't think they have a functional prototype, so probably difficult to predict a qualitative comparison to other types of motion. Honestly my guess is that it's not directly comparable to anything else really, because you typically don't have to output energy during the "off-phase" of walking. Maybe like having a rubber band around the bottom of your foot which you're also holding in your hand?