I used a borrowed one a couple of years ago with my then-18mo DD. It's a bit tricky and you'll need the cooperation of the person sitting directly behind the seat while installing it. I think with an almost 3yo it would be great. My 18mo hated it because it restrained her but an older child might be more cooperative. It does come with a video that shows you how to use it. I must confess I didn't watch the video!
We bought them for our flight overseas, and they just barely fit around the business class seats on our Continental flight--however they were so tight they didn't lie flat against the seat, so it was uncomfortable for the kids. It's hard to explain. I don't know if there would be the same issue with a coach seat though.
Personally I wouldn't go out of your way to get one if it's going to be an inconvenience. We made a 2-hour flight when Hannah had just turned 3, and it was fine with just the regular lap belt.
Re: CARES Harness?
We bought them for our flight overseas, and they just barely fit around the business class seats on our Continental flight--however they were so tight they didn't lie flat against the seat, so it was uncomfortable for the kids. It's hard to explain. I don't know if there would be the same issue with a coach seat though.
Personally I wouldn't go out of your way to get one if it's going to be an inconvenience. We made a 2-hour flight when Hannah had just turned 3, and it was fine with just the regular lap belt.