I'm so very hesitant of workflows-as-a-service: they just seems like a fantastic way to get really locked-in to some incredibly specific vendor; add in the fact that if you're required to maintain geographical-jurisdiction of your data, or you have constraints about 3rd-parties having access to your data then you're more-or-less out of luck.

Also they all seem to charge so very much for what amounts to a fairly straightforward service...