>> ROI function is available only for full frame cameras.
That is how I too interpret the update notes for v1.4.4.
ZWO probably implemented ROI for the full frame cameras because downloads of full frames through WiFi can take a lot of time, not to mention the memory usage and scaling the image for the tablet's display.
That being said, reduced ROI could be useful even for the smaller APS sensor cameras when shooting small galaxies, since it can substantially reduce post processing times.
Currently, Astro Pixel Processor (APP) does not do just-in-time cropping (that I know). To save time with stacking, one has to use APP's batch cropping tool on images from a camera like the ASI2600 or ASI071, including also pre-cropping the master calibration frames. With a typical galaxy that is shot using an ASI2600 and a 500mm focal length OTA, most of the image ends up being cropped away. If ASIAIR can emit a frame-centered ROI of fixed size (so calibration frames and light frames cover precisely the same pixels), it can save a lot of time.