For me I found a Buff just didn't work with 2 days of chin growth and was just bothersome. To be fair the weather was not windy and I wore a wide brimmed cloth hat.
Sleeping bag liner. I thought this would solve the problem of needing just a little more warmth from a 20f bag, to prevent going to a zero bag.
Just a freaking hassle to get in and out of, it's just a big cloth sack, and unfortunately, for me, did not provide the warmth I needed. Supposedly adding about 10-15f of comfort.
Although...some of the reviews are great, (that's why I bought one) so it must work for some folks.
I can't say my Sea to Summit liner keeps me warmer but it certainly keeps my bag clean. In the summer on a warm night I have crawled into only my liner. Later in the night, after the temps drops, still in my liner, I slip into my bag but don't zip it all the way.
using it as a summer bag is a pretty good idea. I can't stand to sleep hot, so determining what to bring before the hike is always problematic. I've been using a old army style "nylon poncho liner" for really warm summer nights.
The summer nights in the blue ridge (Virginia) are getting warmer every year (and more poison ivy at the highest elevations!), So a 40f bag of the 80's has given way to a top cover of some sort, to account for the cooling off in late night and the dawns thermal inversion cooling. It seems breakfast is only time to bundle up anymore.
I've switched almost exclusively to quilts, and can just get by with a 30f quilt from June-september, but only if the temps are going to drop to at least 50, otherwise, it's just a top cover, such as the poncho liner.
IMO mid summer hikes in the blue ridge, avg elev +- 3600' are getting less and less fun due to the rising temps. Grayson Highlands/Mt Rogers NRA (nat'l recreation area) gets above 4000', as does dolly sods wilderness (WV) so the nights are more comfortable for sleeping.
Oh, man! I love my Buffs! And I have a trimmed beard.
For me, it was the Sea to Summit cups and bowls. I found them to have a lot of static electricity and they attracted every piece of forest debris within 10 feet! I couldn’t keep them clean no matter what I tried.
Yeah I like the idea of a Buff and they are light enough I might still take one for auxiliary warmth and wind protection but so far I have found it to be somewhat annoying to wear and not the must have item it was billed as. My son had a full beard and had the same issue.
Another disappointment is Jetboil cookware using the pot stand with the MiniMo. I have loved my original "Flash" so without too much research I got my son a MiniMo and some of the other Jetboil cookware for group (2-3 people) cooking on our backpacking trips since it supposedly simmered and might perform better at altitude. We tried the now discontinued Jetboil titanium fry pan on the pot stand on a MiniMo and found it to be totally unusable. To control the heat particularly with titanium you have to move a pan and the flux ring would catch on the pot stand and tip the stove. Often the pot stand would come off the stove. The new JetBoil fry pan doesn't have the flux rings so I'm guessing we are not the only ones to have this problem. We has similar problems with the 1.5 liter Jetboil pot being too unstable to be comfortable with and ended up just ditching the idea of cooking in a pot with that setup.
Another more minor disappointment was that the piezo igniter on our the MiniMo just would not work at 10,000 feet. It seemed to spark but it would not ignite the burner. It works fine at sea level.
The MiniMo itself is an ok all-in-one if a bit heavy and expensive but from our experience it's not the greatest for group use beyond heating a small amount of water.