Considering Facebook which is part of the Prism system still sees all the who talked to who for how long data

and that It's tied to phone #'s and thus totally non-anonymous,

and that authentication is optional and not well indicated

and that data is storred unencrypted and then backed up to the cloud

and that the client is closed source so could easily be instructed to silently drop encryption and know one would know...

It's really kinda hard to call it "secure". or even "better then plain text"

So for me not secure, and not verifiable (closed source).

A false sense of security is worse then no secuirty at all.