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.
First off, there is a reason they are discounted 70%. Buy a high end quality down bag and you will never regret it. I am still using the same North Face down bag I bought in 1972. No synthetic insulation is as light, warm, compressible, or durable as goose down. The only property the synthetic insulations have over down is retaining some insulation value when wet. After decades of trying unsuccessfully to develop synthetics to match the properties of down, the industry flipped the script and developed a method to treat down to be resistant to moisture (Quixdown® is one).
For affordable bags I have a hard time not recommending the Black Ovis bags. On sale they are around $130. they aren't as light as a true down bag nor compress as well, but they don't pretend to be either and fill a spot for a relatively cheap bag that could be used for road or backpacking. Even for truck camping the browning and it's 8 lbs seems insane. That and a rating of -20 makes me want to call BS immediately.