On my machine it’s consuming about 0.5% - 1.0% of cpu time, which is higher than zerotier in the same machine (almost zero).
Tailscale does a lot more things than just tunneling though. For example, on default installation it’ll catch all outbound dns request on the machine and route them through MagicDNS (100.100.100.100).
Who cares if it already exists, just make it.
Also consider the possibility when the other, more popular projects got enshittified. Now the fleeing users have an option to switch to your project. It actually happened on one of my side project. I made it because I want to try building my own version of X. It got ~2000 users, but later down the road, X got sold to a new shitty owner that waste no time to enshittify it, and my side project suddenly grow to 20,000 users overnight.