Some quick feedback:
1) I swipe the trigger to exit full screen, no problem. But the trigger doesn't let me enter full screen mode. It would be useful to have the trigger toggle between the last full screen mode and normal mode. I did program a Gesture Control gesture to toggle Immersive, so maybe that's a good enough workaround.
2) I'm able to use the keyboard if it was already open before I entered full screen mode. I can't dismiss the keyboard due to the back button limitation, but the keyboard does work. Also, DocsToGo's context menu has a "Toggle Keyboard" item, so I'm able to open and close and use the keyboard in that app. But I'm unable to change the cursor position in a document while in full screen mode.
3) Not being able to use the back button or execute a "back" gesture in Gesture Control when in immersive mode is really annoying. You also can't use the menu button. But I think enabling the "back" function is the #1 feature I'd like to have.
4) I can't open the notifications when in immersive mode. If I execute my Gesture Control gesture to open notifications, nothing happens, and when I exit immersive mode, the notifications are already opened. Force Immersive Mode
has the same limitation, and the dev hasn't been able to solve it.