Oil is the most expensive component in fuel and this is where the supplier will try to cut corners. If you are one who really likes to run those engines their hardest, adding castor to your typical LHS fuel will allow needle settings closer to peak. I usually add 4 ozs per gallon of store bought fuel. Sig castor is all you'll need, a quart will treat 8 gallons.
Since I began using castor, I don't bother with after run oils.
Mixing fuel from jug to jug is OK too, just be sure to use a good quality [and large capacity] filter in the jug.