You'd think 10 slots would be enough, but once I started punching in my ID, debit/credit cards, loyalty cards (I only have five grocery store cards), etc., they all filled up pretty quickly.
What I liked was the fold-out double-sided window holder for your ID; I put my driver's license on one side and my public transport card on the other, which makes it easy to turn the public transport card inside out to get through the turnstiles. All in all it's a good wallet with some nice features, but you might run out of slots if you have a lot of stuff.