Personally, the rest system makes sense to me. If we look at loss of hp as being loss of energy and vitality (until that last few critical hp), it jives very much with my own experience in sustained exercise. At first short rests have an effect, but as the sustained exertion continues, short rests have less and less of an effect, and longer ones need to be taken. An hour into mountain hiking, a short rest does wonders. Two, three hours later, the same rest hardly seems to help. It feels nice when you're not doing anything, but as soon as you start hiking again, the soreness and tiredness returns. As a matter of fact, I'd adjust the system even further: first 10 minute rest gives you level x2 hp back, second 10 minute rest gives you level x1 hp back, third gives you nothing. An hour long rest gives you the level x1 hp rest back, and the eight hour rest resets the whole thing.
Of course, I don't need all the complication, so I'm just as likely to go with the system as detailed by the playtester. But, yeah, I totally buy how it works. It fits my experience.