I am not a fan of those at all. And, they won't help you on the plane. My 4 year old DD (only weighs 33 pounds) is still in a harnessed booster and I take it on the plane. I have travelled with 2 seats before and the best advice is to get luggage wheels and hook them together.
Now, since I only need 1 seat, I put the seat on the wheels, use a bungy cord to attach and DD sits in it and she gets pulled along! No need for a stroller! You should see the looks we get.
Anyway, I have just put the seats in the closet. Not great, but I wouldn't compromise the safety of travel by not having the seat I am used to.
Good luck, but take the seat.