I recently used this bag for a 3 night hike. Temperatures were around 45-50 every night. I also supported my temp readings by checking with www.weather.com before and after my trip for the area I had hiked/slept. However, I was a little chilled when the temps hit about 45 (while i wore smartwool socks, polyester underwear, and polyester tshirt). I was using a big agnes insulated air core and my back/whatever was touching the mat was fine, however, my feet, parts of my legs, and parts of my arms were cold. I am a slightly cool sleeper but have never had a major issue with temp ratings. Normally i'm too warm by morning.
Other things to consider before i went to bed:
-I had a large, warm, spicy dinner.
-Did about 8 hours of hiking and climbing that day
-Was more than well hydrated
-Slept in a tent with other people and a rainfly
I liked the stretch baffling system a lot because it allows you to shift around as if in a normal bed. However, I looked up the specs on the MontBell website to find that there is 10oz of 800 fill goose down total in this bag. The bag does not contain a draft tube for the zipper (a small flap that covers it), and obviously no draft collar (most bags this temp rating don't have one). I looked on Marmot's website to find the specs of the Marmot hydrogen (30), and it uses 11oz of 850 fill down. Although only one oz more, it is higher quality down, resulting (in my opinion) quite a bit more insulation. Marmot also EN tests all their bags. I could not find anything about whether or not MB EN tests their bags or not. I've also looked on the Sierra designs website at the Nitro 30 and its fill with 12oz of 800 fill goose down! Same fill as MB but 2 more oz....thats an eighth of a pound more! My wife has the women's version of the Sierra Designs Nitro (the Spark 30). I climbed in it and there is a HUGE draft tube and zipper guard. the loft is twice the size of the MB ss3 and i was instantly sweating!
I regretfully returned my bag. I believe I will pay more close attention to not just the type of down used but also the fill weight of the bag. If two bags have the same fill, then more down=more insulation=more warmth. Common sense I'll never overlook again.