The feature list reminded me of Tailscale so I went looking and found this on their website: https://www.netmaker.io/resources/tailscale-vs-zerotier

Their comparison graph at the bottom seems to indicate that the differentiating features between their product and Tailscale is that you can't self-host (ignoring the existence of headscale) and that WireGuard support is limited. I believe the latter point refers to the default Tailscale configuration that connects every node with every other node, whereas NetMaker allows different network configurations.

However, Tailscale ACLs should allow you to reconfigure the network into shape you want, so I'm not sure if that criticism still applies. Their claim that "data will pass through their relay (DERP) servers fairly regularly" also seems suspect, as that's only the case for networks where UDP traffic doesn't flow between clients despite STUN/TURN, which is very rare in practice.

The only advantage I can find is that NetMaker has a richer free plan and that they use the WireGuard kernel module where possible. I'm not sure why they didn't lead with that.