The term "rank" in the question implies a comparison and an evaluation of relative merits.
To answer this question, I would make a list of characteristics that are generally accepted to be important in a defensive weapon of this type and perhaps add one or two characteristics that I personally felt were important that might not make the generally accepted list.
Then I would make a list of defensive weapons that are generally intended to fill the same or very similar roles as the defensive weapon in question and that fall into the same general price range and the same general caliber class.
Then I would rate/rank the defensive weapon in question against the other defensive weapons intended for same general application/role.
To answer this question, I would make a list of characteristics that are generally accepted to be important in a defensive weapon of this type and perhaps add one or two characteristics that I personally felt were important that might not make the generally accepted list.
Then I would make a list of defensive weapons that are generally intended to fill the same or very similar roles as the defensive weapon in question and that fall into the same general price range and the same general caliber class.
Then I would rate/rank the defensive weapon in question against the other defensive weapons intended for same general application/role.