The Secure Kid LX/300 has nice regular push on LATCH connectors, easy to get OUT of the car in a jiffy, especially. Maestro has basic old hook on things, a lot more of a pain. Secure Kid DLX/400 has *self retracting* LATCHes, so you plug them in, sit on the seat to install, and it actually gets tighter while you drive. Of course, top tether all of them, that adds a level of annoyance, but it is what it is...
Anyway, the DLX/400 weighs a little more, because the LATCHes are kind of heavy, but it's not a huuuuuge deal considering the easier install.
They are all the same pretty easy seatbelt install.
All can be used on the plane, which is the safest way to make sure it gets to your destination, and the wide belt path makes it reasonably easy to install (recline the plane's seatback for easiest tightening, route the belt, tighten, and then re-upright the seatback).
If you go with a regular booster, tuck it in the overhead for safe keeping