I've always used Echo oil and never had a problem, no carbon, no plug fouling.
I will say tho, some of the good luck may be because there is no ethanol where I always get my fuel. Only time I strayed was yesterday, put the oil in my can, go to a closer station since all I needed was saw gas, figured I'd check it when I got home just because. I'll be d++ned if there wasn't ethanol in the gas which I refused to use and will slowly add it to my truck to get rid of. Went to my regular station and hoping they hadn't switched, nope....just good ole gas still.