This is the smallest extant member of the clarinet family. It is pitched a minor sixth above written notation, and is a minor seventh above the standard B-flat Clarinet. At first glance, the odd key of A-flat seems out of place. Why is the instrument not in B-flat a full octave above the normal instrument? The answer lies in size. A few B-flat Piccolos were built, but due to their small size, human hands were not able to play it comfortably, so an instrument pitched a major second lower was constructed. Even still, larger players find in the instrument uncomfortable. With the A-flat Clarinet there might be some advantage to using a German style instrument with its simpler keywork. There also exists a slightly larger instrument in G, but it is far rarer (though easier on the hands).
Chances are you will not have this instrument available at your disposal. I only know of two pieces in the orchestral literature that use this small clarinet, and both of those are parts that are usually covered by the E-flat Clarinet. In European band works, the instrument is more common, but I have yet to see it in American works. In fact, I have never personally seen this instrument even at musical instrument trade shows.
The sound of the instrument is quite piercing and shrill, but would make for a brilliant and exciting addition of the climax of a work or in a turbulent, violent section. As with any super-soprano instrument, the constant use can be tiring to the ears of the listener and to the mouth of the player.
If the instrument were made available, exciting possibilities can be dreamed of, but at this stage, I wonder if the super high single reed sound would be better if the new Piccolo Saxophone were used.
Dance of the Sugar Plum Fairies for A-flat Clarinet and Contrabass Clarinet (and not Octo-Contra-Alto as the video says)
Duet for A-flat Clarinet and Octo-Contra-Alto Clarinet (this IS the legendary Octo!).