- FAIL Galaxy Tab 4 7" (SM-T230) Android 4.4.2
- FAIL Galaxy Tab A 7" 2016 (SM-T280) Android 5.1.1
- SUCCESS Galaxy Tab A 9.7" (SM-T550) Android 7.1.1
- SUCCESS Galaxy Tab A 10.1" (SM-T580) Android 8.1.0
I don't have any Android 6 device at hand, but this is consistent with @regecks statement "On Android, the root was first added in Nougat" (which is Android 7).
This is going to be problematic, as there are still devices currently for sale on Android 5/6 (such as the aformentionned Galaxy Tab A 7", which doesn't have a replacement on some markets).