Familiarity: I've used it once or twice and have initial impressions
Bag is a little too big. When you get out of the saddle your knees tend to hit it, on my CX bike at least.
On the MTB, this thing seemed pretty awesome. Didn't have any knee knocking while in the saddle, but if you get out you will get a little. With that said, it isn't nearly as obnoxious in comparison to on my CX bike.
Bottom line, great for endurance MTB riding/racing (where you may not be jumping out of the saddle as much), not so good on a CX bike. Maybe a road bike would be OK?
Can't speak about longevity, but definitely seems nicely made. Also, very spacious. Just too big for my CX bike.
I guess I'm gonna have to get n + 1 going on with my top tube bags now for each bike!