I just completed a thru hike of the island of Madeira with my newly acquired atom pack. I had a single hipbelt and I was more than happy with it. Was hesitant at first with a single hipbelt pocket but I must say it was plenty. It kept my Swiss army knife, headlamp, (large) phone and snacks just right. The zipper and materials were waterproof enough to keep everything neat and dry. Bonus points for being able to use the pocket as a stand alone mini pack cube.
The only little things that I noticed were maybe "suboptimal" (and that's pushing it) is the fact that the removability made the hipbelt jingle a bit, and also the way it wasn't firmly fixed made the use of the zippers pretty much impossible with a single hand.
Apart from that, I'd say 96% satisfied. Well done Atom Packs.