They use mechanical keyboard type switches. (a little square box with a plunger on top).
They work fine and do click. I have Seimitsu buttons on my cab. I like them, but sometimes miss the concave shape of older style buttons.
If mounting in a wooden panel, it needs to be fairly thin. I used to route the back of the CP out, but on the last couple I glued a top layer of 1/4" mdf to a 1/2" layer that has the area for the nuts cut out.
The Ultimarc Gold Leaf buttons are a bit shorter and still retain the concave shape.
http://www.ultimarc.com/goldleaf.htmlI remember there being several people on the boards here who didn't allow enough depth for their pinball buttons and ended up using those instead of standard ones.