After buying one of the recent USMC coyote with mesh insert bivy bags I finally decided to order the 3 Season and cold weather bags that go with it.

I am 5'10 and the cold weather bag fit me fine, but the 3 Season regular length(5'11" and below) was snug on me once I started wearing heavy socks and some sort of head covering so I switched to the long length(5'11" and above, same length as the cold bag) and it fit much better.

Sample size of 1 regular and 1 long, but if you are ordering the bag without trying on and are anywhere close to 5'11" I would go with the long length since there isn't much weight/bulk penalty over regular.

So far in playing around with it, the USMC bags are not quite as roomy as modular sleep system components.

The mss light outer bag/heavy inner bag is reversed in the USMC system. I think the mss has the more logical system on that.

I prefer the USMC center zipping bags over right hand mss zippers, although the mss single zip for combined components is handier.

Overall, I like the USMC bivy due to the wired mesh face area. I do think the mss bivy is simpler and quicker to get in and out.