Search for reviews on Rokslide. I think “Mike” who often posts there was an early use of a prototype when he did a circumnavigation of Mt. Rainier in ultralight mode. I think “Mike” is a MT game warden.
I haven’t actually used that bag (so I guess I could get flamed for posting my comments, but I am sincerely hoping they help in some way). I do have some informed opinions based on my personal (sometimes odd) perspective, in the dark ages during a span from 40 to 50 years ago (I started rather young) I did numerous solo long distance bike tours in various regions of the USA and Canada and I have Nunatak gear and I’ve spoken with Jan on a few occasions. I’m a big fan of Nunatak. Also Katabatic.
Have you communicated with Jan at Nunatak? Very straight shooter.
Personally, I hate being too hot at night possibly even more than being too cold (within reason).  One advantage of a traditional DOWN quilt is the ability to be comfortable in a broader range of temperature conditions by using it more or less as a blanket. IMO the Sulo compromises the temperature comfort range more than I would be willing to accept when traveling in civilized conditions (bike tour) in the USA or similar environs.
Personally, for bike trip use, I would never trade off the weight of a zipper or a couple of straps (2 – 6 oz and slight bulk?) for a design like the Sulo vs. something like a katabatic quilt unless I was confident that I would not overheat in the warmer conditions I might encounter while still being warm enough with all my clothing on (but I also don’t like sleepign with lots of clothing).
Personally, I’d go with a top quality traditional 30 degree quilt that offers more ventilation. OTH if I was doing a multi – day self supported wilderness hunt and wanted the most compact lightweight emergency sleep system to carry at all times, then I might consider a sulo. Because then the downside of being too warm is dwarfed by the upside of surviving the night without getting dangerously cold and complemented by the low probability of ever needing to use it. But that is just me with my view of the world.
On most bike trips if conditions are going to be a bit cold you can usually beg, borrow, buy or find something to improve warmth – either with more insulation below or above you. But I find it difficult to “get more naked” to cool off if my sleep system is too warm and does not ventilate well.
On one bike trip I remember sleeping under picnic tables in a plastic tube tent and searching for old newspapers to use for additional insulation on clear nights in E. Oregon because it was going to be a very cold….in September…..and I refused to pull into the occasional “youth hostel” I rode by. Back then I had a lightweight synthetic bag and mailed my big heavy tent home opting instead for a plastic tube tent because it wasn’t rainy (SMH)Â I don’t know how i survived. LOL.
