I'm with Graham on this.I drove petrol and diesel tankers for quite a few years and as I filled my generic tank at the depot the "BIG" brands,who were shouting about "Cleaner" this and added that and so on and so forth,were in the bay next to me filling their logo carrying tankers.The difference in what they were pumping and what I was pumping? Zilch .Plus the fuel I was loading,on many occasions, was been taken to a branded pump.And if anyone was able to add any aditives while I was top loading,well they must have been invisible.
It is the same with any other product.Whether it is bread,gas,diesel,washing machine,breakfast cereal,television set.Few manufacturers,many brands.
Plus any product must meet certain standards for it's application and if you use the oil that meets the standards required by the tool,outboard,vehicle etc. etc.that you are using then there will be no problem,doesn't matter the brand.