I don't really see the point of a rolltop small-sized bar bag, you either need it for general load carrying so probably want something bigger or you want a bit of extra convenient-access storage, in which case you don't want a rolltop.
I recently bought the standard top opening version of this bag, it's OK but agree on the fixed strap position being a pain. I also found cinching down on the straps completely squashes the foam pads so they don't help with creating a gaps for your fingers when riding on the tops.
I also have an Ornot cannister bar bag and it's a lot better (but crazy expensive with import duty & shipping), I use that on my gravel bike but wanted a cheaper alternative for my road bike over winter (to give me more room for stashing jackets/layers/spare gloves/extra food etc.) the Restrap one just about works for that but depends if I can get my Strada light securely out-front mounted, if not I'll have to look for another solution (to be fair it probably wouldn't work any better with any other bar bag due to the straps)
I bought one of these earlier this year (also have their smaller cannister bag and bigger 'bar bag). I love this roll top bag! I've used it in all weathers on my end-to-end ride, and I've found it to be the perfect size for bits and pieces you might need during the day: hat, glasses, wallet, lock, snacks, light jacket, etc.
I find the strap stays done up properly, although I find the Fidlock to be somewhat fiddly. I replaced the foam blocks with slightly thicker items... that makes it much easier to take on and off the handlebars. I always use a cheapo (Ebay £5) handlebar "space saver" to act as a bumber bar.
This little bag is one of my favourite luggage pieces!
I don't really see the point of a rolltop small-sized bar bag
I do - ime the smaller and/or more rigid zipped cannister bags can be awkward to get things in and out of and roll-tops adapt to the amount inside well. Stuff bouncing around in a bar bag gets annoying. All the bar bags I have that I like and use most are roll tops, 3l up to 10l size (the Ortlieb and Roadrunner are faves). The Carradice zipped roll is good as it's rigidity comes from the dowel support not the material or pattern, but it's still a fixed volume bag.
(this one doesn't seem that great though)