People like to talk about getting nature mints, subskill swapping items, but what about the concept of swapping a Pokemon's type to its other type, if it has one?

Would this be too powerful? Just useful, neither too strong or too weak? Or just not useful in the slightest?

Obviously, this would change the Pokemon's berry, meaning you can potentially take a Pokemon to an island dedicated for that berry, for example, swapping Ralts to a fairy type, allowing it to be used on Cyan Beach with favoured berry! Maybe you've got a great Swablu you don't want to evolve, because you'll lose that favoured berry on Cyan, but with this item, you can keep it as flying type. Same with Pupitar!

What Pokemon would you use this on?