Sainsbury's has the same thing - 20p cheaper. Tesco has it as well, I know because we bought it from Tesco but now I can't find it on their website.
It's very nice. I like it. But in most instances it's not really worth spending a lot extra on butter. Is it?
I would probably use this where the butter is a key element of the dish, but not for a bog standard sarnie.
https://en.wikipedia.org/wiki/Sole_meuni%C3%A8re
Our fishmonger sells small Dover soles. Too small for restaurants to want, especially with their huge prices. But the fish are lovely and one is perfect as a portion for one person. We buy a lot of them. People are often impressed by getting these at a dinner. They don't realise that they're not expensive.

You just have to mention Dover sole to have people swooning. (Actually I don't think they are all Dover soles anyway - more probably sand soles, but they look very similar to the untrained eye.

And there's really no difference in the taste.)
I'm trying to be a bit more careful with money because the minimum let period for most properties (including this one) is one year so we have this place until October, but we get our own place back at the beginning of August. So, we'll have two properties to pay for including council tax - that's a crippler - and utilities, etc. I've offered all my cousins free holiday accommodation - within commuting distance of London - between the start of August and the end of October.
It's just how things work out sometimes and you have to do the best you can with the hand you're dealt.