not a stroller/seat, but....Hi,
We have flown twice domestically and twice internationally with our Britax Roundabout, and we use it on the plane. It is great to know Meg will be safe in the plane and in taxis and cars once we arrive.
We use a backpack especially made for car seats to carry it, and the bag fits a whole baby bag inside it together with the car seat. It is a bit awkward and heavy trudging through airports with it, but not terrible. (I travelled the Tokyo subways with this system by myself, carrying the baby and two bags in addition, and I didn't keel over.)
The Roundabout is 18" wide, and the airlines we flew said their seats were only 17" wide, but I read a lot of online reviews of the seat in which users had used the seat on the plane with no problem, so we tried it. It fit just fine. The only potential difficulty is that the person sitting in front of you will not be able to recline if you use the seat in rear-facing position, and you will not be able to sit anywhere that would block another passenger's exit from the row or through an emergency exit.
Meg is used to her seat like your little one is, and I think this really helps make travel easier. She sleeps comfortably, and understands that there are times when she just has to sit in it and buckle up. We take a sling, too, for bfing and cuddling, but she is in the seat for most of our air travel. Thank you, Britax!
When people make comments (and they *always* do!), we just say that we will be so happy when the airlines make a good, easy, standard, and SAFE way for babies to fly! I think it's good to have that kind of reality check sometimes.
Hope you find a good solution. We looked at the Sit-n-stroll, too, but it just didn't seem to hold a candle to our comfy Britax.
Kam, mama to walkin', talkin' Meg