Gameshark Pro 3.0 for Gameboy Color questions

[romanaOne]

Is there a manual for this thing anywhere?

I have tested it with A Bug's Life and it seems to work ok.
But Inspector Gadget Operation Mad Kactus crashes even if I do not apply any cheat codes.
The game works fine plugged directly into the GBC.

Are some games incompatible with Gameshark pro hardware?

What is the switch for on the back? I discovered the button is reset, but the switch doesn't seem to do anything.

 

[Lumstar]

Pokemon Crystal acts buggy on certain Gamesharks. I don't know much about the later special edition.