I have to wonder what the FAA thinks of these devices. I would certainly request to move to another seat if someone next to me started installing a modification that holds the tray in the down position. Worse, it looks like the devices can only be removed by a key - quick, we’re about to go down into the ocean, please find the key to remove these devices that make it harder for me to leave the plane before it sinks...
For those who desire knee room, please choose seats right behind the emergency exit rows on the wings. Those seats do not recline, and virtually every airline lets you pick your particular seats these days. Or even better yet, choose an airline that gives you the right amount of legroom.
I think the key is there for size comparison. But I would tend to agree - it forces the tray table to be down, which would make evacuation difficult.