I use a few of these - simple file manager, simple gallery - on (my wife's) devices which are encumbered by custom Android shells (Samsung and Sony to give a few examples) which make it harder than necessary to perform certain tasks. They are complementary to whatever is installed on these devices, they're not in the way, they're free (from F-Droid) and I don't really care about that orange theme since I only use them occasionally. If you have an AOSP-derived distribution like LineageOS installed there is not much need for this type of app but for those who are stuck with custom Android shells like Samsung's Touchwiz and Sony's Xperia some of these 'simple' apps can come in handy.