I got the smallest Black Diamond at REI 6?, 8? years ago, Love it. It is not large. Doesn't unzip fully so loading it is more of a challenge, but on my back riding it is the best pack I've used by a lot Unless it is fully loaded, I often forget I have it on until I arrive. It is also narrow enough at the top that I don't see it using a short helmet mounted mirror.
I don't recall it being advertised as waterproof but I have never arrived with wet contents unless I forgot to close the zipper. Very well constructed adn thought out. I have not done anything besides use it and it is virtually as good as new. (Actually conderably better since I added ties to hold a U-lock in the sleeve behind the neck, keeping tie lock portion close to the sleeve. Also added many square inches of good reflecting tape.)
The test I consider critical that it passes is the clipboard test. A standard letter sized clipboard fits and isn't too hard to get in and out. Once in, capacity is barely changed.
Ben