It's about the same size as the RS Convertible Carry-on (21x14x9) I already have. It looks like it would be more comfortable to wear, partly due to the padding on the hip strap and partly due to the suspension system.
Both of them have multiple zipper pockets, many of which do not have double zippers, so are not easily secured. The Eagle Creek one should fit as easily on its side in an overhead bin as the RS one and my roller bags do.
The price would have to go down substantially for me to try this bag. It would be my major bag and I'd have a cross-body tote as well. Fortunately I have lots of family to pass my mistakes on to.
Last year I got the Afar backpack (20x12.5x8.5), but I couldn't get the total weight down below 15 pounds and I couldn't manage to make it comfortable on a domestic trip test. The main issues were the thin and too small sternum strap and the thin and unpadded hip strap, unlike the newer version linked.
I keep yearning for something as comfortable as the very simple ski touring pack I bought in Amsterdam and used for 4 months back in 1977. Of course, I only packed about half what I take these days, even though it was a fall and winter trip. I also had a cross-body bag.
With a back and knees that are now 40 years older, it may not be the packs that are the problem! I should give up and stick with my roller bags, but I'm always intrigued by something new.