Unlike Camtasia 2 for Mac, ScreenFlow 5 is only able to perform full-screen capturing. This has a significant impact on choosing the right screen resolution in recording. A recording using the native resolution for an iMac'27 (2560x1440) would result in unclear, and therefore unreadable texts. It is thus recommended to make the recording in a reduced resolution, say 1280x720 or 1920x1080.

Somehow the recorded video clip will still be in the 2560x1440 resolution, I don't understand why this happens, though. You will then have options to export the clip in 2560x1440, 1920x1080, or 1280x720, ... etc.