This is a fabulous backpack for carry-on traveling. We have taken our Ospreys on several trips including one to Europe and one to the Caribbean. The only plane we have had trouble with is the Boeing 767. This plane has 2 seats at the window in the main cabin and 5 in the middle. The ridiculously tiny over head bins are deep enough for a regular backpack. The osprey will fit if you put it sideways. This is also true of regular roller bags- they will only fit sideway. Such a stupid plane design.
I recommend small packing cubes with this backpack. But you will easily go over European weight limits of a carry-on if you aren’t careful.
The smaller daypack has pockets but they aren’t big enough really for a drink when it’s full so that’s a downer. They should have made the pocket stretchier but otherwise it’s perfect for carrying a camera, drink, jacket, and whatever else you might want for a day hike or city tour.