it can't be used during take off or landing, the baby only fits till their head reaches a certain point so for small children, it might last till 3mo old... but otherwise... yeah.
it's a very niche product that I would just never use. I mean it gives the illusion of a way to hold your baby out of the carseat safely on a plane, but if turbulance hit, I see problems and risks. Really, in terms of where baby should be when traveling, for me, air and car is the same... babies and children (though obviously an age without a seat in a plane is different for me than in a car because of crash dynamics and only 2-pt belts on planes) should be in a seat the whole time unless getting a diaper change/going potty or being nursed and burped (that's the one time I'd be fine with giving a bottle in a seat... you just don't know when and how fast turbulance will start and you can't pull a plane over for feeding)
Now, at such a young age, with skulls still forming and needing such frequent feedings, I'd hope that they wouldn't be on a plane for more than an hour or two at a time... and I'd almost prefer stops over a direct flight if the total air time is going to be more than that, but that's just me.