
NEMO
Disco 15 Series
Spacious for side sleepers; bulky, temp rating optimistic.

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It's legit. The reason it's so cheap is that it's only 650 fill power, which means it's quite heavy at 3 lb. 3.5 oz. For hiking/backpacking generally lighter gear costs more. For reference, I have a mid-range 20-degree bag that weighs only 2 lbs and cost me $200 a few years back.
No it's legit. It's a closeout item (like most of Sierra) so Coleman is just trying to get rid of it. 650 is good, but not great fill power. it's DUCK fill, so there's a chance it'll smell a little... ducky when you get it wet. Note that it is a LONG size, so if you're under 6', it may fit a little big. 20F is the LIMIT rating, so that's the coldest you'll wanna consider using it to survive. ("Comfort" is listed at 28F which is kinda the real lowest temp you wanna use this at ). They don't list it, but there's a chance that this is still a leftover from before the PFAS ban. Probably not a big deal, but something you should be aware of.
That's my simplified explanation and suggestion based on the rating, but it wasn't a definition of what the rating is. There is a lot to unpack about sleeping bag ratings and how the test is performed that I might not have the bandwidth for given *\*looks around\** I have too many sleeping bags to test it and review.
I'm more than cool with you disagreeing with my opinion. If you would like to give forth your own suggestions to the OP, well you don't need my invitation.
Peak is colemans backpacking budget line and pretty good all things considered. It wont be the best, but its enough to get you rolling.
They brought back the Peak1 name. It's OK stuff for what it is. A bit overpriced for what it is.
I am a known collector of sleeping bags. I have more than 20 and 1 is a North Face Cat's Meow i bought in 1989, so I have a bit of experience on the subject.. I got the 0° Coleman Peak 1 from my work's incentive site. I would not have gotten it otherwise as I have Sea to Summit, Marmot, kelty, (pre-bass pro) Cabela Instint bags, etc... I took it out my Peak 1 on my November hunting trip. Temps were in the upper teens/ low to mid twenties at night. I had a sea to summit liner and a Mr Buddy Heater at the ready to use but never needed them. I was hot in this bag. I mean, half zipped up and still hot. I was shocked. I mean shocked. The only Coleman gear I have is a stove and a lantern as their gear ain't what it use to be.. and this bag out performed my expectations. Now. I was on a cot with a memory foam pad. I was dressed well. Do with this as u may as I have a slightly different bag. I am a cold sleeper tho. But my Peak 1 has more power fill down than my kelty and marmot and it looks very well made. This bag is coming on many more trips.
I got a modular sleep system at the thrift store about $14 so I use that when it gets very cold if it's going to be 30 to 40° or more, I'll use my 20° Coleman bag just since it's lighter, but the sleep system is actually really quite nice, if very heavy. It's been nice for very cold weather. I'd love a quality, light, very cold rated quilt or bag but I can't afford it for a while unless something washes up at the thrift store again. In warm weather I use a hammock I also got there

NEMO
Disco 15 Series
Spacious for side sleepers; bulky, temp rating optimistic.
Hammock Gear
Classic Burrow 20°F
Budget king; very warm but heavier than ultralight.

NEMO
Disco 30
Spoon shape for side sleepers; prone to zipper issues.

Western Mountaineering
VersaLite
Durable, very warm; premium price, too hot in summer.

Katabatic Gear
Alsek 22°F Quilt
Versatile 3-season quilt; secure pad attachment, high price.

Ranked #1
NEMO - Disco 15 Series

Ranked #1
Kelty - Tru.Comfort Doublewide 20
Ranked #1
Enlightened Equipment - Revelation APEX

Ranked #1
NEMO - Disco 15 Series

Ranked #1
Feathered Friends - Egret UL 20/30

Ranked #1
NEMO - Disco 15 Series