I seriously love this pack, and it has instantly become my go-to as a personal item on the plane (under seat) that can also be used as a super-light daypack at my destination. It's incredibly lightweight, bigger than you expect, and made of what feels like really sturdy materials, while still being "smash-able" -- you can really scrunch it up when needed, and yet when full, it will mostly stand on its own. Somehow this bag has flown under the radar, and I think if more people got exposed to it, they would go nuts over it. It's that good!
HOWEVER, the lack of a luggage pass-thru seems like an astoundingly huge 'miss' to me -- it's literally the ONLY negative I can say about this bag so far. Put a luggage pass-thru on this -- an effective one -- and I will literally buy another one to get that feature.
In summary, I can't express how much I love this bag -- it has literally replaced an entire stable of bags I've been using as personal items for international flights -- but it is a real drag trying to mount it to my rolling carry-on (I use an external strap with a buckle to get it to stay attached to the telescoping handle of my roller). I know it would add weight, but please consider adding some method of luggage pass-thru. Other than that, I so far can't recommend this highly enough -- just get one.