I've been using Zerotier personally and professionally for some 10 years or more and as a network engineer I love the product, and have long recommended it. I've compared it to Tailscale, and while Tailscale has a lot more enterprise-y features, they too miss some key features of Zerotier like being able to use route ANY subnet IP addresses, not just limited to their 100.64/10 addressing Tailscale limits you to. Tailscale also requires you to use an oauth account for users, which has never been compelling for personal use.

I also believe it was around before Tailscale, or at least I knew of it before Tailscale, but I've never seen a compelling need to move from Zerotier to Tailscale.