I do and had a fascination with them.  I do have a few Best and Falcon SFIC cores a Schlage LFIC and Everest cylinder, a couple Medeco locks as far as non typical locks go. I like YT videos by Lock picking lawyer and Bosnian Bill as well as a few others.

I also have Schlage LFIC (or FSIC as Schlage calls them). I quite like their simplicity as there are no special calculations to enable a control key. In fact, I modified standard blanks to make control keys !

I also have some Sargent LFIC, but I have difficulty getting the pinning right to enable a control key but to prevent the operating keys from removing the core. I guess I need more practice...

Well, that's interesting.  My late father has a special padlock that is really thick and has the combination paper attached.  It took me doing to figured out how to unlock the padlock