Just make sure it has the sticker showing FAA approval. It will be the easiest way to be assured you won't have any issues.

We do most of our flying on US Airways and in my experience, they are pretty particular about approved seats. Our son is past the car seat stage now but FAs checked his seat on at least three occasions. We were on a flight where the FAs got the captain involved because parents were using a non-FAA approved seat.