...2. I see 2 mags in the pic, along with 2 springs?
3. When I went to a youtube of guys using this, they just dropped the slide in with a different "pin" and it was ready to go; they didn't do anything with springs?
Those appear to be recoil springs which I assume are of different weights to tune the system if needed for different velocity ammo. The recoil spring is pre-assembled on the recoil spring guide rod and placed in the slide as a complete slide assembly. Therefore you would not see the spring being changed in a video showing swapping the .22lr slide assembly for the 9mm slide assembly as they are only showing swapping complete assemblies.