Well, I mean, three is many faces to have. Three is the number. Four is too much and two is not enough unless it's followed by a third. And five is right out*. I actually had a Man-E-Faces when I was a kid. It was a pretty good toy and the face switching never got old. Need a Wolverine-like berserker? Covered. Need a robot to team up with your Autobots or plot with the Decepticons? Done. The human face would probably work well with superhero action figures as either a hero or villain from the future. Like many of my childhood toys, I have not one clue about what ever became of it.
*I'd like to take this moment to apologize to Monty Python and the entire fandom for that butchering of a classic scene from Holy Grail.