Many games, and even the odd demo, picked up on the presence of a Multiface. In order to stop illegal copying (or in the case of the demos, just to look smart), they would then refuse to work.
Most notorious of all was [[Elmsoft]]’s [[Zap’t’BallsZap't'Balls]]. Run it with the Multiface plugged in, press the red button, and you’d get a rather rude message. Ironically, one of the much-vaunted cracks of Zap’t’Balls was accomplished largely with the Multiface’s latterday rival – [[Siren Software]]’s [[Hackit]]. See BTL 2 for more.
To get around this, Romantic Robot put an on/off switch on the Multiface. When it was turned on, you could make copies, reload games saved with the Multiface, and use the toolkit. When it was turned off, you couldn’t. Seems fine.