I can't speak to the actual security, since that'd require a lot more knowledge that I possess (and an audit). Open source can mean more trustworthy, but doesn't per se mean it's more secure unless someone has actually gone through and looked at the code. Still, it's always good sign. I found a Hacker News post talking about it, and the Tenta folks give a little more detail about some of their plans and what-not (although that thread is from awhile ago). At the end of the day, it's a question as to whether you trust them enough to use their VPN and DNS servers.
So far, I'm not sure what could instill in me, an average tech-savvy user, such a trust with what little material I can access with my limited technical knowledge. I think an alternative DNS is a cool idea, and I'd like to give it a shot with opportunity present. The reason being not security — much like an average user, I'm inept on the idea of Internet privacy and don't see a good reason to worry about it so long as I'm below the radar — but merely the capacity to use unofficial top-level domain names.At the end of the day, it's a question as to whether you trust them enough to use their VPN and DNS servers.
That's not nothing. And there's certainly something to be said for having alternatives out there, and making other developers take notice.