Awesome! I wasn't sure how putting a sticker/label/vinyl thing on the top of a button would work but at the price he charges it's definitely worth a shot. I like how his standard buttons sheet has 4 $0.25 so I can replace them if they wear off.
It's on top of the button insert, it's still under the top of the button. In other words, you don't actually feel the decal. For my money, I go with the inserts from GGG, and translucent HAPP red buttons. They look like this

And I prefer my buttons concave, so that's why I go with them. If you are ok with convex, there are a ton of options out there for you.