- Yes, the GSX installer is one and the same, the only thing that activates the L2 features is your license. When the sites says GSX is required to use GSX L2, it's ONLY from a licensing point of view, to clarify you cannot buy "just" an L2 license and expect it to work, you need to buy the base GSX as well, that's what "Expansion" means.
Nothing to do with the installer. The same page, when describing the installer for L2, says it includes both GSX and GSX L2, precisely for the reason to tell you don't need to DOWNLOAD 2 "things", but you surely need to BUY 2 things.
- GSX, like all our FSX/P3D Products, is SOLD IN TRIAL, which is why you are not asked for a key during setup: how could you be able to try it, if you needed a license to install ? GSX, like all FSX/P3D products, is activated from within the sim, in the Addon Manager menu.
- The Universal Installer can't install FSX/P3D Product. It doesn't need to, because their installer can always be freely downloaded. The install feature is only for MSFS Products, that don't have a Trial, and since download links on Digital River expire after 30 days, the Universal Installer solves that problem of users losing their installer which, again, was only a problem in MSFS, not FSX/P3D.
- The Universal Installer CAN also be used to Activate/Deactivate FSX/P3D Products, it's just an alternative of activating within the sim. And can also be used as an updater. The program it's exactly the same just with different interfaces depending which icon you use to start it.
If you start with with the "Update" icon, it will download only the files that needs to be updated, for all products, then it will quit, and yes, this is normal, because the Update interface is supposed to be used to quickly update everything, possibly before starting a flight, so it doesn't annoy you with a useless extra confirmation at the end ( there's nothing to confirm, after everything is updated, the only meaningful choice at that point would be exiting, which is what the program does ).
Instead, if you start it with the "Installer" icon, you are in control of what to Update, what to activate, deactivate, read the manual, etc.