I own a small double flap, at first I was worried whether it would look not proportional to my height as I'm about 5'8"...but the fact is that actually both small and m/l are look like small bag on me hahahahaha so I might as well just use it as a small bag! both small and m/l are gonna require using a non-fullsize wallet if you wanna fit more than a phone, so there's really not that much of difference in my opinion, another thing I have noticed, the chain length are actually the same for small and m/l, but it appears to seem longer on the small because the bag is a bit smaller, and I love wearing it single chain.