The question of VP's quality control is the issue. Sure you probably get a good 60/40 blend 95% of the time but that means you get a tank full of bad fuel twice a year.

For only 3.5% discount it isn't worth the risk. You can save that much just by driving better, or only ever filling your tank to 1/4 full or by checking your tyre inflation more often, or by walking to the corner shop and post office.

When I take my vehicle out, it's worth far more than 3.5% to have the confidence that I will get to my destination 100% of the time.

George