I have one, and it's about as thin a design that I can imagine one can possible do to accomodate 3-5 cards and several bills. Here is why.
You want the pouch to hold its form, and for that you need quality leather of a certain thickness. On the other hand, to minimize bulk, you want as few pockets as possible. You don't want cards mixed up with cash because it's rather inconvenient to have to separate them as you access one other other. That leaves you with a design with a minimum of 4 layers of leather.
The Atelier Pall does add another leather strap on top of the minimum 4 layers of leather, so it's slightly more bulky than say another design without a strap. But I think the strap is what set it apart from other designs with tight pockets to keep things from falling out. It make accessing cards and cash a lot easier. I find it about as convenient to use as my wallet. Other designs you really have to take your time to neatly fold cash to make it work. That may be OK occasionally, but day in day out it's annoying for me.
I usually carry 3 cards and 3-6 bills, but I have stuffed 5 cards and 8 bills in mine and it still worked quite well. But for 3 cards and a few bills and the iPhone 5, it's thinner than my old wallet. I don't think there is anything out there that's better for me.
Best of all, the thing is beautifully made using really nice leather. I think the iPhone 5 will become obsolete long before this wallet wears out.
