I've been using the Silca Mattone for about a year now and like it pretty well. Initially I had trouble getting it attached to the seat but I've gotten better at that with practice and honestly don't take it off that often. I do wish it was slightly bigger. Initially I struggled to fit a tube, inflator, lever, and single CO2 cart. I got a TPU tube and that made it easier but it's still a tight fit. I've had zero issues with any BOA, either on the bag or on shoes so don't worry much about that.
That Almsthree bag looks like it's bigger and still minimalist. Would like to see one in person.