I have not tried ZeroTier yet but have come across it quite a bit lately. What advantages if any would you say it has compared to just running a simple Wireguard VPN into your remote network?
It very much needs an identity provider, only they implement it themselves instead of outsourcing it to Google/MS.
On Tailscale you also need to whitelist machines in the web console. There's probably an automated way to do it as well but I haven't looked into it since I only use it for a few static hosts.
I've migrated from ZT to TS about a year ago because ZT was much slower (network bandwidth-wise) and CPU-intensive than Tailscale on my setup. YMMV.
You can self-host the ZeroTier controller which is the identity provider and you an do so without breaking interoperability with the rest of the network.