The tip for creating a long screenshot is simply to specify the area to be checked for stitching together.
The app will then automatically composite one frame at a time from the captured video.
It is a simple mechanism, but it works better than expected.

Of course, the app also supports compositing from still images. Simply select the images you want to combine and specify the areas to check.
The combined screenshot can be checked and saved within the application, and can also be exported to the photo library from the share menu. (If the image is too long, it may be reduced in size.)