So given that the word doesn't really apply to hardware, I believe they used it correctly (100% means the set of things where it makes sense to be used) and are not misleading. In fact I strongly dislike some of the "open-hardware" marketing of some previously mentioned devices, when that is obviously false and misleading.
This likely would also mean that it can't be flashed, so if you care about future maintainability, this is also a negative -- it can not be updated/fixed in the future, which may or may not make sense depending on what part we are talking about.
But if there are some kind of signature validation then it gets even more complicated (like e.g. iphone screens knowing if they are from apple or not).
This is a "necessary but not sufficient" thing.