It's only for android.
[EDIT]: https://www.facebook.com/surespot/posts/614633905213667
26th June: "Just sent first successful surespot encrypted message from iPhone to Android."
1.) It's not open source
2.) They want to charge for certain features that are free in surespot.
(on top of the $100k they're already asking for)
3.) They wont let you run your own server