Hi - worth an argument on this one!! Remember you dont get 'out for nowt' and being a local bike shop next to a Tesco we see a lot of two strokes bikes with running issues, no power and/or blocked exhausts - the oil is cheap for a reason and does not always burn leaving harmful deposits in the exhaust/engine which eventually, like yor arteries, get blocked - then the heart attack happens!!
..and as for Morrisons, dont even go there! We make a lot of money out of customers who use Morrisons fuel and oil - thanks Morrisons!!
Personally - its worth the extra - you have been warned!!