Mk Ultra, I used my tan Merlin on deployment unzipped as a blanket. While the fabric was very luxurious to the touch I wish I'd still had my Wiggy's Desert Bag. The Wiggy's was warmer, more rectangular in shape vs mummy and unzipped into a square shaped "comforter." Several years ago while in the field during summer I got too cold in my Hennessy with just my OD Merlin. A buddy gave me the Patrol Bag, (green one), from his MSS. It saved the night being warmer and I slept like a baby. The Merlins feel great, are light and pack small but I don't recommend them for your BOB. They are better than nothing but unless you get a super deal............ no, not even a great deal. I got the Snugpak OD fleece liner for my Merlins to help with the lousy temp rating. The liner really added wieght and bulk. The liner didn't have a zipper either! Nothing better than unzipping your bag, peeling it back and instead of rolling in you have to do the "mud skipper" (WW's coined phrase) crawl just to get in. You already know how well other fabrics slide against sueded fleece! Aghh!
Tan Merlin with OD sueded fleece liner;
The Wiggy's FTRSS Overbag is IMHO far superior to the Merlins! If you NEED a cold weather bag and pack space is at a premium I agree with WW, get yourself a Kifaru POD. It'll open up a lot of space inside your pack, for more cold weather gear, fuel, food, and clothing. The POD becomes an integral extension of your pack. You will not look like a hobo with shit hanging off all over your pack, or that you made the wrong pack decision or, even worse, like Linus dragging your woobie behind you down the trail. (Not that you ever would!) You won't get the dreaded "hamstring slap" or "bum bump" as you move out with the bag bouncing off the back of your legs either.
I really like both the Mil Issue MSS and the Wiggy's FTRSS "systems" (Wiggy's way superior to the MSS! IMHO best there is currently.) for people getting into this stuff or that are ready to try winter camping. They are good solid systems, both are synthetic, fool proof, and both systems give you options for year round use. Lotta bang for the buck. CON, niether of the pack down small......but they're both a lot of bag.
If this wasn't what you needed lemme know.