My wife says I sleep like a rotisserie, constantly rotating.
I found that I sleep better in my AA because in a mummy bag I'm more confined. Also, with the straps around the bottom of the pad I'm less likely when I rotate to take parts of the bag with me, so I'm not twisted up in the bag as much.
I use my AA with a hooded skaha, so the face opening follows me as I thrash around.
All in all, I prefer it to a mummy because I thrash around.