Not for backpacking but I have one of the 0 degree bags I use for truck camping. I'm not usually a mummy fan but it works well for me. I've spent many nights in single digits in the bed of my truck. The zippers work well and you can cinch down the hood pretty well. That said, it's not anywhere near what I would consider a backpacking bag. It's heavy and doesn't compress worth a dam.
We have a few of the 0° bags. Heavy and super bulky, once out of the bag they come in they never went back in, not a bag I'd want to carry far from a vehicle. But two out of the three of us were comfortable at ~ 10° laying on stall mats in just our base layers. The third person is cold anywhere without heat though. We don't usually camp in fall/winter so I don't have any other bags to compare it to yet.