First Aid - Action: Allows units to enter the wounded state where they wriggle on the ground instead of dying. Allows their team members to stop their bleeding and revive them slightly, with instant effect (think: BF2 revive).
First Aid - Simulation: Allows units to enter the wounded state where they wriggle on the ground instead of dying. Revive takes quite a long time. This is an alternative to the Action system, so don't need both of them. This explains the internal name for this module, which is Alternative Injury System (In fact, the "Action" code is run as well as the Simulation code if you put a Simulation logic in the mission).
First Aid - Battlefield Clearance: Enables the drag and carry options. Doesn't mind which other FA system is in use, but drag/carry is really rather pointless using the Action system, since you can instantly revive people.
Medics, in all cases (vanilla, Action, Simulation), are the only ones that can really heal people of damage. Action/Simulation revive just stops bleeding and wakes injured man up.
Lots of bugs in the system regarding JIP and respawn. Just give it time to get itself fixed...