> If there is a gadget that does a thing that no other gadget does, what does it even mean for the interface to be "terrible?" How can you even know if the interface is terrible, given that a better one has yet to be invented? Maybe the interface is as good as it can be for the tool in question.

That's just a taste judgement, and you can decide the interface sucks on a one of a kind item quite easily, and people often do.