Gerald W.wrote a review of Rab Ridge Master Nestor Bivy on September 21, 2014
Familiarity: I've used it once or twice and have initial impressions
Purchased this bivy as a lighter weight alternative to my 1-man Alps tent. This is about 1/2 the weight. Recent use in the Sawtooth Range, ID, camping at about 10,000ft. Clear days and nights that dropped into the 30's. Haven't tried it in the rain yet.
Incredibly light weight for a tent at two pounds; disappears inside my pack. Very good breathability. Contrary to the others, I didn't have any condensation in the morning, even with temps in the 30's. I could feel the tent breathing as I laid there, which is a first in tents for me. Also, I was warmer than I have ever been at those temps than with my normal 1-man tent. Love the long zipper that allows me to easily squirm inside, but it does require a shimmy down to grab the end of the zipper and tent to be able to zip it back up. I chose the olive color and it is dark enough inside for sleeping in late.
There is no vestibule, so you need a pack cover. There was enough room in the bivy to stash my boots above my head, but I am 5'9". If I was over 6' that might get tight. If you are claustrophobic, this still might be too tight for you. The tent sits about 6" above your face when you are laying down on a 2.5" inflatable pad. I had enough of width at 175lbs and a 34" waist. I was able to side sleep without discomfort. Bigger people should try before buying since it is a slim footprint.
I would hate to spend an extended period of time during a rainstorm or blizzard in it since you are laying on your back with no window above. This bivy is for sleeping, not for spending a day unless you really don't get stir crazy. I knew that was a tradeoff when buying it for ultralight backpacking, though. At least the awning design allows for looking out with rain protection if you have no other choice. If I knew it was going to rain, and I had to shave weight from a standard tent, I'd probably spare a few ounces so I could pack a tarp to act as a vestibule for sitting and cooking.