Great questions. They are convex. I'll add this to the description as it's kind' a important. I don't have my caliper here, but according to my ruler the shaft is about 1 3/8 deep. They can de mounted in a 3/4 inch panel with 1/4 inch Lexan and still have plenty of room for the nut.
They also have an opaque underlay in the middle of the buttons, which give them a frosted appearance. This should avoid the issue everyone is having with the Happs translucent buttons.
Lastly, they are designed to use an LED, so there's no jimmy-rigging needed.
-Mike