I can't remember which shop now but they had an own-brand veggie pasta thing, I think it was ravioli so I put that in the trolley. Further on I spotted a similar Gino D'Acampo thing so I thought OK that's probably better so I'll have that as well. Nope. The supermarket's meal was much, much nicer than Gino's brand. Sometimes you're just paying more for the name.
That said, I do tend to go for "Extra Special" or "Taste the Difference" rather than their value goods.
Another thing I've read, but not encountered myself, is that there might be different levels of pricing within the same shop. Eg if you buy X off the usual shelf it costs more than if you can find exactly the same thing in the World Foods Aisle. Anyone experienced that?
Edit: Asda does a Miso and Cornish Sea Salt Flavoured West Country Butter. Oh man, that is so good it's hard to stop me just hacking bits off and eating it straight from the packet. Obviously I should try cooking fish in it - probably do that today. Maybe baked tattie with a creamy smoked haddock filling. Heaven.
