I don't have it, but I've looked at it. It doesn't hold much at all and I'd say it's more of a wallet on a chain. I'm anxiously awaiting the St Germain BB release, which looks like a beautiful small bag.
It is comparable to any wallet on a chain regarding size. I considered buying this also, but once I tried it on I didn't like it at all. The leather is too soft for such a small bag it had no structure and I didn't feel that it would hold up.
As Havanese mentioned, I would wait and see what the St Germain BB looks like.
Ah yes, I've watched some YouTube vids on the Saint germain bag itself, not the pochette. And the reviewers said that as its a soft leather, it moulds to your hands.
I would like a more structured wallet on chain just like the YSL woc