One reason that is good enough for me: HN is a bit of an echo chamber. It's maintained by a specific VC with specific opinions, which already was a source of some controversy. While I don't see a problem with the existence of opinionated media, I do think it's healthy if we have alternatives. And being "european" is specifically beneficial, because it brings with itself a somewhat different perspective.

I'd probably use both (unless the other one dies, of course — just because it's useful doesn't mean it will work).