Seriously...?
http://grammar.ccc.commnet.edu/grammar/adjectives.htm
"Adjectives are words that describe or modify another person or thing in the sentence."
I.e., "...wouldn't consider them
completely useless" pretty well defines that since the uselessness is not considered
complete, that there are instances in which they might be considered useful. Then he goes on to describe the circumstance in which he sees a use.
EDIT: The corollary of this is that MM would consider the useFULness of the product to be incomplete, as well, and could likely define instances in which he found them so.
Just in case:
http://www.merriam-webster.com/dictionary/corollary