The wife bought me one for my birthday a couple weeks ago. I like it a lot. Not too big, not too small, great for commuting. Looks completely natural on the 919. The rear strap hooks could be tweaked a little to fit the seat curves more perfectly, but once you get it settled in, I don't see it going anywhere. In words of Krusty of the Clown, "I heartily endorse this event or product."
She found it on sale somewhere for $90, so shop around a bit... They also sent her two by accident (?), and she hasn't sent the second one back yet... She claims she just hasn't gotten around to calling them, but I think it's because she knows it would fit perfectly on the 599 she has her eye on!