She'll sit in it quite nicely while we're eating (with the tray off, since she can barely reach it). She likes to slide over to one side and prop her foot up on the smaller tray (even with the belt on). She needs a little help getting back up from that position, though.
We also got her a bumbo, which is a bit more her size, although she doesn't have as much of a tolerance for it (maybe because it doesn't let her slouch and slide around like the other one? uh oh).