If I'm looking for a zero degree bag, it's because I need it in winter, or at high altitude. Either way, personally, I prefer a mummy bag. Mummy bags cut weight by tapering at both ends. An added bonus of the tapering is that the fabric of the bag is kept closer to the body, trapping additional heat.
In short, if you're car camping, these are fine. If you're getting out there, these are way, way too big and bulky.
Day 1 of the 12 days of Crap- about 1 minute in, sold out.
Day 2 of the 12 days of Crap- about 45 seconds in, sold out.
Day 3 of the 12 days of Crap- about 30 seconds in, antechamber of doom.
Day 4 of the 12 days of Crap- exactly 22 seconds in, antechamber of doom.
Day 5 of the 12 days of Crap- missed out on even trying- "I'll only be a second".
Day 6 of the 12 days of Crap- I fell asleep, and didn't deserve a shot at it.
Day 7 of the 12 days of Crap. I have completely given up hope.
Day 8 of the 12 days of Crap. 30 seconds. Antechamber of doom. Nothing I do makes this go any faster.
Shooting for about 10 seconds I guess, which means somewhere around day 9 or 10 I may get lucky.