I can't believe no one has reviewed this awesome bag yet, so I'll try to give a pretty thorough one.
I've had this bag for a month now and finally got a chance to put it to the test. With a weekend trip to my folks, the forecast calling for snow on the east coast, and an overnight low around 30, I couldn't think of a better time to try the Nitro out. So here's the results of my little field test.
I'm not entirely sure how companies rate sleeping bag temperatures. But here is my experience with this bag. First off - I am typically a warm sleeper, as in "sleeping next to you is like sleeping next to a heater." That said I set out deep into the backyard to make camp, threw on a midweight base layer (IB260 top, paty Cap3 Pants), some [lightweight] running socks and crawled into my bivy and the Nitro.
The hood cinches down nicely around the face, however it would've been great if they had given up an extra ounce to add something to make the opening a little softer against the face. Where the cords were drawn tight was stiff. However, I did have this thing cinched down to "blowhole" size around my mouth and nose.
I was warm when I crawled into the bag and stayed warm through the night. It was definitely cold when I woke up and I was still pretty comfy - I could feel some of the coldness coming up through the ground. I was sleeping on a Therm-a-rest Neoair, and should've had a Z-lite mat under it, but didn't. So my insulation from the ground wasn't quite what it should've been. The only thing that was cold were my feet. I blame that on the lightweight running socks, had I been smart and put on a pair of midweight wool hiking socks I think they would've been fine.
There was plenty of frozen condensation inside the bivy a testament to the freezing temperatures, but the down stayed dry. I certainly wouldn't call this bag's liner waterproof, but it did its job against the condensation. Even after being woken up to the sound of my father's laughter as a snowball exploded against my bivy and I was showered in frozen condensation, I was able to shake the ice off the Nitro.
I got up and went in the house to find out that it had actually dropped to 23 degrees overnight! No wonder my feet were a little chilly and I could feel the cool ground through the sleeping pad!
A few other thoughts and notes - The stuff size say's 17 x 7in. That's the size of the stuff sack that comes with this bag. It can actually be compressed much smaller than that, probably around 12 x 6in. Maybe less, I should've measured. It also comes with a nice mesh storage bag, like any sleeper in this price range should. The foot vent is nice, although it was unnecessary in my latest experience. There are also nice stiffeners along the main zipper to prevent snagging which work well.
The flex baffles are awesome. I'm convinced this is one of the things that helped me stay warm despite going well below this bag's rated temp. I had been looking at Montbell's bags for this, but their regular bags are only good to 5'10" (I'm 6'). So I was really excited when this bag came out. Eliminating the dead air space, while still giving me the ability to move around a bit in the bag was definitely helpful in keeping me warm.
I would recommend this bag to anyone without hesitation. Its light, warm, packs small, and certainly earned its 30 degree rating with me.