It's a userland implementation. This is for the in-kernel implementation. It should be faster. Also, there are some comments that the userland version is rather hacky and probably should be transitioned away from once you can.
"pfSense® Plus software version 21.02 and pfSense Community Edition (CE) software version 2.5.0 include a major OS version upgrade, a kernel WireGuard implementation..."
I'm currently running it in an OPNsense box to serve our internet needs. I have a connection that without VPN can push through about 400-800 Mbps, and when I put the VPN on for all traffic, I can still push 400-800 Mbps through my connection.
The in-kernel version can do the same with less CPU usage, and can probably drive multi-gigabit connections without any trouble.