Difficulty ratings make sense. Stuff like non-BP props can simply be dropped in a level as decoration, and therefore would be BEGINNER. Stuff like BP’s that require lots of integration into your project would be ADVANCED. And it’s not really as subjective as people say. If you don’t know how to modify a BP to get it integrated with your own stuff, you’re not at an ADVANCED level yet 
This rating would help prevent consumer shock when they buy an pack and they don’t have the prior knowledge to actually use it yet.