ZeroTier charges by device. Tailscale charges by user.

ZeroTier is a lot cheaper if you only need to connect a single device for each employee. It gets a lot more expensive if you have a lot of devices.

Tailscale is the opposite. Cheaper if you have a lot of devices, but if each employee only has a single laptop which needs to be connected, then it's a lot more expensive.

Tailscale's documentation is way better and walks you through it like a beginner. ZeroTier's documentation assumes you are already knowledgeable about networking.

I think the ZeroTier free tier is much more generous. I also like the client app, which lets you be connected to more than one network without switching. The API is also nice... I've hooked it up to an Ansible play, and it works well.