This is especially helpful for users with metered connections. You don't have to send ALL your traffic, only the ones destined for LAN will get sent.
If you've got a working OpenVPN setup, then it probably makes sense to just stick with that. I'm guessing the real gains are only to be had when you want to overhaul your setup anyway.
I haven't bothered setting up wireguard yet, but on paper it looks a lot better and when it's stable I suspect a lot more people will jump on board.
I've sized up its current functionality as useful for replacing OpenVPN, but not yet as a general mesh VPN.
This. I've installed it on Android just because I get a better experience with WiFi switching on when I have a poor signal. And having my SSH connection not break is nice.
super exciting. can't wait to see where it goes from here.
I can only agree. I have WG installed on my iPhone, iPad and use the WG service provided by Mullvad VPN. And it is on all the time since a few months back. I don't experience any connectivity issues, lack of performance or degradation in battery/power consumption. It really just works. Huge thanks to Jason for developing WG as protocol, server implementation and clients.
It's been a while but I tried to do that with ipsec or something like that in the past and I think it was causing problems. With the routing maybe.
No activity since March, though.
There's also official documentation for how a userspace implementation should behave. 
The android version of WireGuard has a userspace implementation for devices without WireGuard in the kernel, which at the moment is pretty much all.
There is also BoringTun: https://github.com/cloudflare/boringtun which is faster
Disclaimer: I wrote BoringTun