The folks at Mullvad gave me a couple days to try their service (Very generous of them, thank you!).
I sent an email to them asking about Wireguard, and how they feel comfortable offering that when the actual project side says, do not rely on this code. Here is the response they gave:\
So I decided to go look at the wireguard project page. It no longer says "Do not rely on this code". It appears that it has been removed. The last time it was on there was August 24th of this month: https