...different seats are different heights, and depending upon the pitch of the seating configuration and whether or not the person in front of you happens to be reclining the seat, you may or may not be able to get the tray table down flat.
The one thing I can say is that generally, with a booster you have a somewhat better chance at being able to use it than with a convertible seat for younger children; those seats mostly have higher side bumpers than boosters, which are usually more upright.
Sorry, that wasn't really too helpful, I know, but I thought you might appreciate some kind of answer, rather than nothing at all.