This version changes the text in a few places to make some ambiguous things more clear (like how authority affects rebel attraction). It also tweaks a few minor things on the gameplay side and fixes some minor bugs. Fully compatible with old saves.
If you're on moddb, I'm assuming you at least know how to look up a tutorial on installing mods.
Stellaris replaces some core files that most other mods reference. You can try using SZ with another mod, but I doubt it will work smoothly. Graphics mods and mods that add/change ships are probably ok though.
This is the full version of the mod. It should be compatible with old saves. If you're updating from a previous version, I recommend deleting the old mod folder before installing the new version.