I picked up a couple of these sticks along with a couple of the Game Elements adapters as part of the same auction. I must have gotten part of a bad batch, because neither of the adapters worked on my Xbox. I tried every 1st and 3rd party pad I had. I don't have a Gamecube to test with, so I don't know if they just don't like my system or if they're broken. On a side note, if you open them up, there's a spot to add a third cable for USB connectivity. I don't think that it requires any other work beside that. I'd found the info on a site a year back, but can't find it at the moment.
As far as the Pro Shocks go, for basic gaming, they'd probably be pretty decent. They're hard to get a decent game of Street Fighter out of because they want to slide all over the place. The sticks themselves have miniature microswitches and do feel arcadey. They can be easily mounted to a metal control panel, so I decided that I'm going to cut one stick off of one controller and wire it to the X, O, square, and triangle buttons of the other and make a mini Smash TV controller. I think they're decent enough sticks for it. The wiring is ribbon style, soldered on both ends. It appears to be solid wire, so be careful not to bend it too much or too often and be mindful that when it moves, it's likely bending at the board-side solder points. You could probably snip the wires closer to the stick and attach a disconnect or splice directly to a longer piece of stranded wire.
The buttons are just plastic caps seated on top of silent switches like those found in Sanwa buttons. The switches are soldered directly to the board, so you'll have to do some desoldering. I'm going to salvage mine in the hopes of using them for a future project. I don't think the terminals are large enough to justify trying to snip the terminals just below the switch housing to use quick disconnects in place of soldering.
I haven't checked yet to see if there are seperate grounds for the stick and buttons, but I don't think that's a very common type of setup.