Don't know what effect these bags would have in a hammock, but I think they're great bags, and the temperature ratings seem accurate. They are tight when fully zipped up, but you can stick out your arms to lessen the cocoon effect. They also zip down intuitively, garment style with a double zipper, so you can also stick out a leg if needed without having your chest get cold. I have both a 2-season and a 3-season. I'm contemplating getting a 4-season as well.
sb11I've been sleeping in a Hennessy for a while. and this bag looks fine to use in a hammock. However, I don't see the value of the cutout arm holes because the arms and shoulders are notorious cold spots while sleeping in a hammock. I recommend a lighter three season sleeping bag or top quilt and an underquilt any time night time temperatures fall below 70 degrees.
hikeasaurFor me, the arm holes are great for venting and for getting rid of that initial sensation of claustrophobia. It's also easier to zip up the bag with your arms out, and to grab things at night without having to unzip the bag. While I love the freedom, versatility, and low weight of quilts (I have both a 20* and 30* from EE), I was always colder using them, especially since switching from a tent to a tarp, and not wanting to use any pad other than a Z-Rest. The Mobile Mummy 3-season not only solved my coldness issues, but in particular they, ExPed, and ZPacks place their zippers down the center of the bag (instead of on the left or right) which is the best location for a zipper as far as I'm concerned. I initially went with the Mobile Mummy because it was the cheapest of the three I could find at the time.
I do agree with you though: I wouldn't sleep the entire night with my arms hanging out either.
I do agree with you though: I wouldn't sleep the entire night with my arms hanging out either.