Having now had the chance to fly on the 321neo in First and E+, it's been an overall positive experience but with a couple annoying quirks:

• First: The underseat storage is very shallow (vertically) - I had to remove things from my backpack and store them in the seat pocket for my backpack to fit
• Economy: The seatbacks are not particularly sturdy and I've had the pleasure of sitting in front of people who like to smash the touchscreen, which jostles the seat. Quite annoying when trying to sleep (or just in general). Maybe it's an unlucky coincidence with fellow passengers, but the one common thread of flying on the 321neo is that every flight I've turned around to ask the person behind me to please tap the screen gently