I think that it would be a much bigger problem if one of the armrest tables were open than if the seat back table was down. The armrest tables are often not very easy to open/close.

I agree that the armrest tables are not very likely to accidentally open while there is a greater chance of this happening with the seat back tables.

Overall I think that it would be easier to get out of the plane with the seat back tray tables, because they are very easy to put back up if they ever did get accidentally knocked down. The movable armrests would make for much more room while moving toward the exit (they can be very easily flipped up).

-Mike