I bought this ages ago. So long ago I can't recall where I bought it or who invented it.

I fitted the ROM and the interface board. The ROM is recognised at boot up.

I have not actually used it, because I bought it to have a look at the circuit diagram and see how it worked.

It is basically bit-banged by the 6522. It does not use the 6522's shift register feature. Just voltage-level shifting and some local power decoupling. Not much, but it is certainly less time to earn the money to buy it than to make your own. Let alone write and debug the software.

One of these days I will get round to formatting a card and loading Elite onto it...