It’s just a hosted reverse proxy with a proprietary server backend, as far as I can tell. I don’t usually trust “free” things lime that. It’s not that expensive to do it yourself, the real expense come in high bandwidth flowing through the proxy which most self hosted applications for personal use don’t really do.

Anyway, with a reverse proxy on the security end there’s a chance of man in the middle attacks depending on the configuration. And on the privacy end, they will have the ability to log all connections. That may be where they’re planning to make money by selling that info and/or allowing MiTM attacks to inject ads like many ISPs have talked about. But “free” stuff usually isn’t actually free in the long term even if it is now while it’s being tested. Usually just takes a sale to a large corporation for it to become less free even of the original intent wasn’t to do that.