Where to buy 100m 12mm Stainless Steel anker chain ?

[MapisM]

completely agree about the stability,
but with two ankers you have much more chance that your anker is tangled with a neighbour anker chain.
In Cavtat, the quay is curved...

Yep, I've never been in Cavtat, but I see what you mean of course, and can't argue with that.
Actually, the only occasion when I can say to have thouroughly tested the two anchors setup for mooring stern to the quay was in ACI Split.
Moored along the outer side of the harbour wall, where several big boats had stealed all the bow lines they could find, because a bura blow was predicted.
The marina folks were useless at convincing the neighbours to give back at least one bow line, therefore, I had no other choice than to deploy the anchors, though on the positive side there wasn't the risk you are talking about, obviously.
And it actually turned out to be a lucky choice, because when the bura blow arrived, it was even stronger than predicted, and some of the other boats had to support the bow lines with the engines, to avoid hitting the dock with the stern, while for us it was just a matter of recovering a bit of chain...

 

[MapisM]

MapisM, that isn't my experience using 12mm s/s chain.

I take your word for that. And I accept that s/s can reduce this risk, AOTBE.
But in one boat, also with 12mm chain, I actually saw it happening.
And also heard from a couple of chaps who experienced that first hand on their boats (though both with a bit smaller boats/chain, 10mm IIRC).
Btw, for what I recall of BA anchor locker, I suspect it's not as good as yours at limiting that risk.
Otoh, B seems sold to the idea, so I guess he will tell us soon about that - all the best to him anyway, of course!

Yep - that is the principal benefit of 2-anchor system in my book, but as you say the occasions when you want to deploy this method are quite rare

100% agreed.
That and full redundancy whenever you should let go one anchor in an emergency, of course - not that I ever had to resort to that so far, touch wood!