I own one. I bought it for my son when he was about 18 months old. I tried it a few times over the past couple of years, but it has it's own issues:

• my son loved to unbuckle the seat belt since it was now easy for him. (I addressed this by bringing a sock with the toes cut off to act as a sleeve over the latch)
• my son sleeps well on planes in the car seat, but cant in this.
• It involves installation that requires fiddling with the tray table of the person sitting behind, which can be awkward.
• If I'm renting a car when landing, I still need to bring a car seat anyway.

I will probably try it again soon now that my son is 3. But, recently, we have simply used the Cosco Scenera Next on-board.