Functional bikes. Not Porn not Anti

Get the skf then. They're about as good as it's gets for square taper. No point in paying extra for a shiny Phil one you'll never see. But I do agree with Ed the un-55 is by far the best value competent there ever is.

and difficult idea to put a "cheap" bb on a 8k€ bike... !

Well, if you think about it, a lots of components on expensive bike are cheap, such as the brake cable, chains, cassette, even the stem.

You don't need to spend a lots of money on cassette, they all wear out almost equally, nor a chain for similar reason.

Brake cable can be hard to tell, the biggest difference is usually housing and the cable housing end (cheap housing end actually create friction).

Stem, you can just get a £15 one that work just as well as a £80 one, the difference is way too small to warrant such upgrade (maybe lose 5 to 10g, perhaps a little stiffer), and even those difference may be hard to notice to some people.

There are some components that are worth spending money on, but a lots of them that are not necessary.

Visualised this, riding your new Tandem, what will you notice? the ride, the components working as intended, the fit? etc.

I will bet actual money that you will have a massively hard time noticing cheap components when they work, the only thing that will affect you is the placebo effect.

Not really sure I'd regard the UN55 as 'cheap'. When you think about it. It's probably had millions in money+man hours spent to develop it over the span of what...25 years? That's a long time to perfect the main spinny thing.
Most unappreciated yet most perfected bottom bracket ever?