Taken it on two trips already and like it a lot.  On all the planes I was able to find space in the overhead compartments, but I was checking out the underseat spaces closely.  I am pretty sure it would fit under the seat for middle and window seats (if not overstuffed), maybe not for all aisle seats.  I like the numerous zippered compartments including the one where you can keep your travel papers and a book and get to them without opening the entire bag.  I also like that when you have to hike across the airport to another gate you can easily use the backpack straps to free up your hands and not be dragging something behind you in a crowd.