Perhaps something like applicability or utility will suit your needs. (Utility saves you five characters, and I'm not sure you'll find a word much shorter.) If you're simply trying to avoid the use portion of your phrase, you can try ease of operation, though that doesn't meet your preference of being shorter.
If you're looking for something more adjectival, I think user-friendly nicely sums up your sentiment (in fact, this could be extended to user-friendliness, though truthfully I think that sounds slightly forced and awkward). However, if you're trying to avoid using anything remotely related to the word use, I would recommend something like accessible or straightforward.