It is still quite expensive, the kernel module is still faster. Performance depends a lot on your kernel version and network card. We measured anywhere from 20% to 40% advantage to kernel module. But we are working on additional performance features, such as using send/recvmmsg and raw sockets.
Thankyou, that is even better than what I would expect. I have been trying to tune around similar issues in tinc-vpn which also runs in user space and depends on newer kernels and code changes to work around.
Why not use XDP?
Look at curvetun, the author used some tricks to boost the speed (PF_RING I think).