The only oil I don’t use is Magnatec, as I’ve seen first hand how thin it goes when warm. Nowadays I’ll use whatever is on offer at ECP in my cars, and change it every six months.
If there was a budget tyre that performed identical to an MPS4, then why wouldn’t I buy it? I’d buy any tyre that was excellent and suited the car in question, which is why the Scoob runs RE070 and the Omega some cheaply nonsense tyres.
Brake pads, tyres, seats etc: these all have physical properties I can tell the difference in quite easily when driving. I’m sure I could tell a car on stale fuel over fresh fuel, but between Tesco and Shell? Nope, I’ve never ever been able to tell and as said above, I doubt 99% of people ever would be able to on a blind test.