NEW YORK (MainStreet) — You are buckled up snugly for the five and a half hour flight from JFK to LAX, but when the plane reaches its 35,000 ft. cruising altitude, matters take an abruptly painful turn for the worse when the announcement is made that the seatbelt sign is off and, kaboom, the seat in front of you reclines at full force into your knees.

Exactly that scenario is why you need to know about Knee Defender, an ingenious - some say insidious - device created by Ira Goldman, a onetime Capitol Hill staffer, now turned inventor who runs a website called GadgetDuck where he sells the results of his brainstorms.

The rockstar is Knee Defender, which the 6'3" Goldman told MainStreet he invented as "self-defense" after his knees were banged up one too many times on a flight.

The concept is simple. You quietly attach the small, plastic Knee Defender clips to your tray table arms -- it takes just a few seconds, said Goldman - and, presto, that seat in front of you cannot recline.

Knee Defender user Robert Siciliano - a well known identity-theft expert -- swears by the product.

"Seat reclines are a violation of my space," he said. "They should only be permissible after 10 p.m. or in rows with extra legroom. And 99% of people completely lack common courtesy and recline so dramatically fast that it's shocking and upsetting."

He explained what prompted him to buy Knee Defender: "I've had a laptop screen cracked when a completely inconsiderate passenger in front of me whipped his seat back. The fact I didn't flip out and air rage, to this day, astonishes me."

Siciliano added: "I use [Knee Defender] proudly with no compunction or remorse."

But there is lingering question: are these things legal?

When the Washington Post asked the Federal Aviation Administration for an opinion on Knee Defender, the FAA responded that there is no FAA rule that would ban the use, except during taxiing, takeoff and landing (when seats are required to be upright, so Knee Defender would not be needed anyway).

Note, however, that not every passenger supports Knee Defender use. For every Siciliano who sings its praises, there's another passenger who condemns it.

For instance: travel writer Mitchell Blatt, who covers China, said: "Reclining is the only thing that makes economy seats a little bit more comfortable. Each passenger purchases the right to recline with their ticket, and the person behind them has no grounds to interfere. If they are uncomfortable--as are many passengers--they should recline themselves."

Malaysia-based travel writer Andy McFarlane said similar: "Here in Asia, and indeed in Europe, reclining your seat doesn't seem to be such a potential ignition of air rage just yet, and particularly in Asia, it is a borderline rite of passage for the majority of passengers. I would imagine that someone using the Knee Defender would be quickly told in no uncertain terms to remove it, or else I can foresee that the aggrieved passenger would remove it themselves if possible. Overall, I think it's a novelty more than anything, which does nothing to force airlines to actually reconsider their seating layout and configuration."

Frequent flyer Dirk Aguilar is even blunter: "Knee Defender is preemptive in assuming that the passenger in front will recline but should not be allowed to. It contributes its own little part to social degradation. In my opinion, Knee Defender should be banned as a tampering device."

As for Goldman he said he has never been asked by a flight attendant to remove the $21.95 Knee Defender.

Additionally, in the ten years Knee Defender has been on sale, there are no reported instances of passengers getting thrown off planes for using them.

The point: Knee Defender is pretty stealthy. Probably nobody will notice it, and a passenger who complains about not being able to recline will be told, sorry, your seat is malfunctioning. If there's an empty seat, he will be moved there.

And as for the Knee Defender user, he can relax - knowing his knees (and laptops!) are safe for yet another flight.

--Written by Robert McGarvey for MainStreet