Any basic functionality found elsewhere would be helpful really. It might integrate nicely, but it can't do much past running a script that would take care of everything (build-wise). Variables? Not really. Conditions? Not at all. Final steps? Nope.
Documentation (at least of API) is not that great. If it is available since atlassian's Confluence seems to be down most of the time. The API itself is pretty weak as well. And weird too.. getting an HTML error response on json request? Yay!
All in all, it's one of the worst tools I had to use in the recent years. It looks like a dummy product, just for the sake of it. But at least it's fast I guess. Or I don't get its purpose.