I agree entirely, except this bag wasn't purchased specifically for MMs, I can't afford that luxury as I don't do MM's as a sport. It has been through Tasmania and N.Zealand where much of the time it was unzipped or even used as a light duvet, been far too hot without the zip. Also used here on my solo nights out when I need it very much 'zipped up'. So it's an excellent compromise.
I might purchase another for MMs (if I start doing them regularly) and have been looking at the PHD's for some time (minimus range), but a lot of cash if it's not something I actually need.