Pros:
-This bag is excellent quality and feels smooth against skin and not clammy or sticky. Sleeping inside with no shirt on did not leave me uncomfortable.
-Packs up super small and had a great quality stuff sack that can be used as night time hanging storage in a tent while the bag is in use.
-Would be a perfect addition to a survival kit, or in an overnight bag for unplanned stays away from home

Cons:
-I would never use this bag in 40 degree weather. The loft is not nearly enough to provide adequate warmth without wearing supplemental layers inside
-this is a one season bag, that season is summer!

Great bag for someone with a budget. Packs down really small, mine got down to about 6x5 inches with the included compression sack. Little nervous about the warmth, but after spending the night in it I have little doubts that it would make the 40 degrees mark if you are wearing a small layer. Really like the bag, there is no way the price/weight/warmth can be beat.

This is a great little bag; packs small and light. I take it on all my summer trips, but would agree that you will need a layer of clothes to make the 40f rating. Obviously since it is a light bag it is a bit on the fragile side. Take extra care when zipping up.

After getting sunburned all over this bag was really nice to spend the night in. The lining is very soft and the bag is roomy as well. I enjoyed being able to move the bag with my whole body getting in different sleeping positions without it getting bunched up anywhere. The only drawback I found was the compression system on the included bag is a little awkward but at the size it is that's no real issue. After my first night in this I can't wait for the next. My expectations for weight, size, and price have all been met with this bag.

Used it in a variety of different temps and kept me warm. Packs small and is light, inside it is soft and quite comfertable and on the colder nights can just about sinch the opening shut to stay toasty

Used this back in the spring season in the Blue Ridge mountains. I made the mistake of not using a pad in combination with this bag and froze my tail off. I was wearing a layer and I believe the overnight low was around 48-50. The great thing about this bag is that it packs down very very small (which suits my ultra-light style). I just ordered the X950 Pro and we'll see how that one does with a little extra insulation and a small pad.

Overall the X650 is a good lightweight bag I would use only in warmer weather.

Took this bag up to Lake Placid last weekend. Kept me perfectly comfortable with an overnight low of 50. I used a sleeping pad and was wearing shorts and a T shirt, so to use it down to 40 a liner or warmer clothes would help but. I like to to be warm when I sleep. This bag is also super light and packs real small. If you're looking for a good cheep summer sleeping bag this is a great way to go.

This bag packs extremely small! Very light pack and you can take it anywhere with you. Its very thin, so it doesn't keep you very warm. Definitely wouldn't sleep in 40 degree weather with this one. Maybe 65+ degree temps. Good summer bag.