After doing some research as a backpacker I am not interested nor impressed with this system. However I haven't used these things hands on but here is my train of thought based on knowledge of how sleep systems work.
1. Claim is made that the bags can be used down to -30 using both bags and bivy. I don't believe that. A sleeping bag is warmed be air trapped in the loft of the bag. Placing one bag inside of the other is very ineffective. What happens when you do this you are degrading the loft of the bags by stuffing on in the other thus losing warmth.
2. Gortex bivy will not add that much warmth and in fact could make you colder. If the bivy is sealed around you and even more so if your face is inside of it. It will cause condensation. The condensation will cause you to became wet and feel colder. The human body produces as about a liter of water during the night from the skin and your respiration.
3. Only thing that I could find on the weight stated that the system weight 10 Lbs. Not in my back pack. Second issue with the weight is that 2 synthetic filled bags will take up a lot of space. They simply do not compress as well as down.
Not that I am an expert by my current sleep system is this:
45 degrees and up: I use a 60 degree Slumber Jack bag. Weight 18 Oz. if I expect the temp to be closer to the 45 than 60 I take a Polartek long johns and a fleece shirt to sleep in. If closer to 60 don't need the long johns and fleece top,
45 degrees to 0 degrees. I use a Monte-bell synthetic bag the Super Burrow Bag. It is rated to 30 degrees and I have comfortable in it without base layers down to 30. I have been cozy in it down to 15 with the long johns and fleece top and a watch cap. While I haven't done it believe that I could with the proper base layer sleep and down sweater sleep in it close to 0 degrees. The weight of this bag is about a 18 oz.
With both these options I use a Thermarest Trail Lite pad or a Bag Agnes Insulated Air Core.
In my opinion again no expert but I do log a lot of bag night. Even though I have a synthetic bag you would be better spending you money on a good dawn bag. They are lighter, compress better, and will last longer. While I like my bag I wish I had waited and saved up a few extra buck and gotten the down bag.
Hope that helps some if you need any specific information on loft and grade of feathers let me know.
