We recently migrated away from our old OpenVPN deployment, and Zerotier was on the table. In the end we picked Tailscale because it’s based on open protocols and more transparent in how they work.

From a different perspective, it appears Zerotier is investing a lot of engineering efforts in maintaining its own protocol, with arguable benefits. Tailscale seems to be deploying new features on an almost weekly basis and are having huge velocity, and to me it just appeared their trade-offs made more sense, and I have more confidence in their business doing great on a long term.