Why did you stop using it?

Well, it seems to be stalled, for starters.

Running a VPN between only 4 machines wasn't that useful, and it needs a central server. I quite like Meshbird's idea of using DHT instead. If it ever evolves to improve its crypto and setup, I might take it up instead.

".. it needs a central server."

There is a PDF by the original author that explains the difference from "VPNs".

A reachable IP address and a TAP device are the only requirements.

For example, two edges can also be supernodes. A third party supernode would only be needed for the initial connection. Once connected, then each can use the supernode run by the other. The third party is no longer needed. No central server.

As for DHT, who runs the DHT bootstrap server?

Do DHT users run their own bootstrap servers?

Do users exercise any control over the DHT? Who does?

By central server I mean a referral hub, yes. But I just couldn't keep one up reliably (in the sense that I didn't want to, since the mesh had to be fairly dynamic in my case).