I have this discussion with the in-laws, mortgage paid and on a fairly decent pension from the police, always shop at Lidl's

we might pop around to see them, have a drink they say , the tea bags are Lidl's and my mrs hates them, she drinks PG tips, The coffee is warm and tastes a little of coffee ( I must admit, not a fair comparison as we have a bean to cup machine and fresh ground coffee always tastes better ) , the Lemonade tastes horrid ( Lidl's V the Sainer's own brand we drink ), we would struggle with Lidl's for drink

We have tried Lidl brand Baked beans, we massively prefer Branston Baked beans to a point that the Ldil's Beans ended up in the foodbank

My youngest daughter can always tell the difference between Cheese, her Fav is Cathedral City, we will occasionally buy own brand Extra mature, she can always tell the difference

We use Butterpack instead of lurpack though

so for us its a bit of a Mix, we mainly shop in Sainer's, occasionally in Waitrose ( we love the fresh almond croissants for breakfast ) then every now and then Tescos, but dont really have a strict supermarket loyalty but will have own brand stuff