To clarify, the userspace implementation is not a benefit, it's just that you can't have a brand new protocol dropped into a trillion dollars of existing hardware overnight, you have to do userspace first as PoC

It does save 2 round-trips during connection compared to TLS-over-TCP, if Wikipedia's diagram is accurate: https://en.wikipedia.org/wiki/QUIC#Characteristics That is a decent latency win on every single connection, and with 0-RTT you can go further, but 0-RTT is stateful and hard to deploy and I expect it will see very little use.