Following a case of air rage when a “knee defender” was deployed in an aircraft in America which went viral in August, sales of the small device have rocketed by 500 percent.
Commercialised since 2003, it protects the very tall from having their knees crushed when people in front recline their seats, but some airlines ban it.
Inventor Ira Goldman will not say how many he has sold or how much he has made, but his little pieces of plastic have already led to at least one flight being diverted when a row between passengers went out of control, and look set to cost some serious legal fees.
But in the world of air travel where every millimetre counts the device divides opinion.
Industry analysts say the problem is not one of individual freedoms but airlines cutting legroom in a quest for profits.
The device is sold with printed courtesy cards the traveller is advised to leave on the seat cushion in front of him as a warning.