I pretty much exclusively sleep with one of my feet sticking out uncovered over the edge of the mattress. Without the warm foot/chilly foot combo, I'd just feel uncomfortable in this bed.
I don't see the problem. The ring isn't solid, it's like a pillow all around so it wouldn't hinder you from that. There would only be a small height difference with the weight of your leg on the soft ring, even seems like it could be even better than a normal bed.
Even if it squished most of the way down, I'd still have my leg uncomfortably raised. But I also use a pillow that's so thin that it barely lifts my head higher than the mattress at all, so maybe I'm just unnaturally well-suited to the flat slab bed shape.