How does it stays closed? With the magnet?

It folds flat. There is no magnet holding it closed. Once it is in your pocket it stays closed. I have never had it come open in my pocket. It stays in my front pocket and is very comfortable.

I'd love the same exact wallet without the leather. Any plans for that?

(If you haven't already found out) Just look up "Secrid Slim Wallet" in the search bar, and you should find one that doesn't have the leather, and is just the metal chassey. I myself am having a hard time deciding which of the two to get, the plain metal, or the same thing but with the leather attached to it for extra space and small amounts of cash space.

What grade of leather is used on this product?

Here is the link to Secrid website where they explain what kind of leather is used in their products. https://secrid.com/en/collection/leather Hope it helps

Will this wallet allow card door readers to function?

So it's an RFID protected inner metal pocket. The most door readers use RFID. So I have used hotel cards in the interior holder and just pop the card out the back whenever I want to get into my room. But the card will not work inside the holder because that would defeat the purpose. I enjoy not having to touch my hotel key card in order to open the door. The leather pockets that surround the inner metal wallet are not RFID safe and hotel cards, depending on the strength of the system the door lock is using will sense the card through the wallet, so that's nice! Additionally, the very large and thick key cards will not fit in the wallet well, inner metal or outer leather. That's unfortunate but I've rarely come across them anymore.