Originally posted by Captain Blue Sky
If an airline crew discovers the use of them (and they do, as it prevents seats from reclining) they are instructed to confiscate them. I wouldn't use them anyway as it will only cause a problem for the person who brought them on board the aircraft.
Captain Blue Sky, that is an interesting story about knee defenders. As far as I know, an airline captain can keep anyone or any thing off his plane. Like the old ship captains, they rule their vessel. He can say, "No plaid shirts today. Sorry." He can even land the plane and kick someone off at his whim. But unless there is some FAA or TSA rule or imminent danger, an airline cannot "confiscate" anything from a passenger and not give it back. Unless you fly for maybe Air China, but not any US carrier, AFAIK.
Your best bet is to involve the Flight Attendants in a situation that might develop into friction. They are all trained in negotiation and mediation techniques.
FAs are almost always great, doing a sometimes tough job on a crowded plane. But I have never seen one tell a pax to not recline, except at a meal (a meal?) or on takeoff/landing. They say "people have a right to recline" or they just shrug their shoulders. After all, who needs to care how long the legs are of the person behind the recliner? Coach class is crowded. As you say, "aircrafts are designed to maximize revenue, especially today." But people being hit in the legs or hit in the head when leaning over to get something from a carryon, it's not right. Or worst of all, my lap baby being hit in the head by a reclining seat.
In any event, I've got long legs and no matter how straight up I sit, on most planes in coach (though not the AA planes that still have the extra room) my knees hit the seatback in front of me as soon as I sit down. I usually take out the airline magazine just to have room. With or without some device, my knees stop any seat reclining. If someone in front of me does try to recline, they go almost nowhere but I get pounded. And geometry being what it is, it is not physically possible for me to stretch my legs under the seat in front.
Sorry for the tone, but a friend of mine who frequents this forum sent me a link to your post (with her own smilie) while I was on the road and now that I'm home I wanted to note my exception to what I think is at best a wrong-headed approach. Airlines should find a better way. It's not just about "comfort". It's about health (DVT) and safety. For example, they could limit reclining or have no-recline sections, all without cutting rev. Maxing rev is fine, but airlines have a responsibility to provide a safe environment in the cabin - health and safety always come first.
Or, the FAs might say, "Welcome to our flight today to Orlando. Please be sure that your seatbelt is fastened. And, when we get up to flying altitude and you want to recline your set, please take a look first to make sure there is enough room - that you won't hit someone's knees or a baby sitting on his mom's lap." But they don't want to say that because then the airline would acknowledge the problem - but they do not want to do that. FWIW.