ROOT is required. Without it, the app will not launch. Problems? Use the EMAIL DEVELOPER link in the Play Store. Today some apps store big files over the internal SD card Typically users have a small internal sd card size while the external SD is a lot bigger
According to the antivirus report, FolderMount is safe and secure. Madmack is the developer of this application which can be found in the Tools category. Over 1M users downloaded and installed the app and its latest release was on Dec 18, 2017.