In my experience, the clasp is decorative rather than functional. Mine didn't want to stay closed at first (one side kept coming loose), but I spent a couple minutes working the leather strap a bit to make it a little less stiff, and I haven't had any issues since then. (I have the large size in Vachetta, have had it a while now... 6 months? A year? I don't remember.) I can pull it open without the key, but that's not a big deal for me.