Ok, I understand the concerns although it could be nice for clarification in the portable vaporizer section.IIRC it was proposed before but the verdict was that using "tags" as attributes was a better alternative (like "pen style" etc...)
That being said, if you bring it to the table again, to be anal, the correct classification would be "externally powered and non tethered" (to eliminate vapes with a power cable, and those with internal batteries) But I already see a problem for vapes that have the butane tank inside them... And what if it's another gaz? What about solar powered vapes? What about.. you see?
When you can potentially end with many unknown categories, I think using tags/attributes is more efficient and flexible than using a tree. See how gmail got rid of the folders and smartly replaced them by tags? It's more powerful as a given item can have multiple tags (impossible with a tree without duplicating nodes or creating some kind of reference/linking)
Maybe said tags should be used more thoroughly and better advertized / put forward?