It does not outshift by itself; you have to command it with the provided switch.
And yes you can leave it in overdrive, and downshift the main trans exactly as you do normally.......... except when the driveshaft rpm falls below the pumps ability to maintain pressure, then the unit falls out of gear. Once it is in shifted, you can do whatever you want in the main trans. And with 4.10s or better, you can drive pretty slow and not have a drop out.
