A dead PP9 can be gutted, leaving behind a black plastic box that can be used for all sorts of things. Very handy, and effectively FOC to those of us who run our old radios with them
I've been tempted to pick up a couple of these myself, if only out of curiosity. The first port of call would be to check the safety, based on previous experience of that sort of stuff. The capacitor used to drop the mains often isn't the correct class X2 type, for example.