Oh, to expand on my above comment, it's not the vaults that make my wallet run away screaming, it's the Metal XX's that are calling my name. ;)
Anyway, the small kevlar vault does indeed work like a charm. The medium is a bit big, but I love the ergonomics of it. I think I'll mostly use the small one, but I have that medium vault in case I accidently find myself with more Oakleys. ;)