I have the SG 15 and I love it. Packs down great and way lighter than anything I’ve used in the past from off the shelf to military sleep systems (iykyk).
That being said I’ve used it when it was maybe 55+ out and it was too hot lol.
I’ve had WM bags before and now have a SG 0. WM going to be slightly nicer, but the loft and treated down for the price of the SG has me sold. I also have a Katabatic flex 15 and I feel like quality is pretty damn close.