I did and the CPU usage on the clients is much higher compared to kernel wireguard or even nebula (userspace, written in go).

Add the fact that it has no advantage over nebula and I stopped using it in a heartbeat.

This is true, on my iPhone 12 mini Tailscale is often the heaviest app (now at 17%) whereas Wireguard never really registered. Strange thing is that on some days Tailscale also barely registers. Could be that the Home Assistant app, which also takes a lot off battery connects via the Tailnet, and it communicates a lot in the background (tracks my position and some other Phone sensors.)