The Aer Day Sling 3 has been the perfect size for emptying my pockets, and still having the ability to carry a bottle. It fits a 500ml bottle just fine. The bag looks a bit fatter than I'd like, but that's exactly what allows it to fit a bottle comfortably. The keyring clip works well with split rings, but the opening's not wide enough to fit a nite ize G-biner, so clipping my keychain on is a bit awkward. I was skeptical of the magnetic fidlock buckle, but it's quite secure. It only opens if you slide it in one particular direction. So far, it hasn't opened by accident. It's definitely designed as a cross-body bag, but the carry handle is really useful for short distance carry. The strap is too long to carry around the waist, but you can shorten the strap by pulling the slack through the buckle and tucking the slack in.