I was using Camtasia Studio 6 for Windows and then I bought Screenflow when I switched over to a Mac. Today I downloaded the free trial for Camtasia for Mac and having been using it all day. I doubt I will ever go back to using Screenflow again. Camtasia for Mac is much easier to edit audio and video than Screenflow, and yes, it has a bunch of built-in transitions (like super easy to add fade-ins, fade-outs, etc., etc.) that make it better than Screenflow. Its kind of Screenflow-ish looking too.
Get Camtasia for Mac now while its the same price as Screenflow and you will be getting a better program than Screenflow. It does not have as many features as Camtasia for Windows...yet, but they say they will be adding many more in the next few months.
Steve