Honestly I pay for the premium even though I use absolutely none of their premium features. At €10/year, it's the cheapest subscription I've ever encountered, and I don't want to store OTP at the same place as my passwords to avoid single point of failure for my most important stuff.

Hopefully they do. Services as important as a password manager should be paid unless you host it yourself. Bitwarden is only $10 a year.

It's open source (both client and server) and there's a third party reimplementation of the server

I pay for it without using the premium features.