Great news. I started using Wireguard instead of OpenVPN and won't look back. Actually it was easy to set up even with DKMS kernel modules but having it in mainline will be great.
OpenVPN works fine, is quite portable and runs in user space. It's quite a lot slower, but is well-tested and can be managed with a Certificate Authority in organisation where that's desired.
They are very knowledgeable and spend a lot of effort in securing their VPN. I contacted them about what I thought was a bug, and got a very thorough answer about why mullvad behaved like that, what kind of threat it mitigated, and how I got the behaviour I wanted together with things I could do to keep safe (which was to update the kernel). Within 6 hours.
I am a very happy customer.