BigBen Gamegrip STG-ONE

Since I hate playing most games with touch screen controls on my phone or tablet, I got myself the Bigben BB325928 STG-ONE Tablet Game Grip (iOS, Android) schwarz .
Hardware wise, it seems to be mostly quite nice. The phone/tablet holding mechanism can fit anything between around 13cm-29cm. Even my Sony Xperia Z1 Compact fits, even though it is slightly to small and therefore not firmly in place. But there is no danger of it falling out of the mechanism in normal use (not playing with the gamepad on its head).
The analog sticks and buttons have a nice feel to them and the analog sticks are at a perfect position for my (normal sized) hands. The 4 buttons and the D-pad on the other hand are to low to be comfortable in a normal position. If you grip the gamepad lower, you can easily use them though. But in that position you can't really use the analog sticks or the triggers well. So if a game requires both at the same time, it could be rather difficult and painful after a while. But since I haven't had the chance to really play with it yet thanks to the software/firmware (more on that later), I can't really tell yet.
L1 and R1 are normal buttons, but the triggers L2 and R2 are pressure sensitive even though they feels like normal buttons with a clear pressure point. If you press really carefully at the bottom tip you can control the amount, but it is really difficult. In addition to that, it doesn't work with the right trigger on my device since it seems to be defective and only after a clearly felt and heard jump of the button, the press is registered as it should (at least hardware wise...).
The Analog sticks are clickable as well. There are also Start and Select and a Home key(which turns the device on and off and starts the pairing together with start) and a slider for the 4 modes.

And now to the software:
The pairing via bluetooth worked mostly without any problems on my Z1 Compact running a rooted Cyanogenmod 11 (android 4.4.4). But from there it is a hard battle. In the Android(2) and Keyboard(3) mode, I can't get anything to work with the official APP. If I enable the STG-ONE IME, an error message appears but otherwise there is no clue why nothing is working.
At least in HID Mode (4), the Gamepad is working... Mostly...
The 4 main buttons are messed up in their arrangement which leads to a bad layout in most games. The right Analog stick is also incorrectly recognized and further messed up through the triggers. Games (I tested with Goat simulator and Limelight root and some PC games) think the triggers control the Y Axis of the left analog stick etc. So playing games like that is mostly impossible. Then I tried Tincore and other similar apps, but they are really complicated and full of bloat I don't need anyway.
So after some research and hours of testing, I present you with an easy fix for the button layout (on rooted devices):
 Create the file /system/usr/keylayout/Vendor_0e6f_Product_0201.kl with the following content:

#This is a key layout file for the BigBen Game Grip to make it work correctly in HID mode.

#Buttons

key 307   BUTTON_A

key 306   BUTTON_B

key 305   BUTTON_X

key 304   BUTTON_Y

key 310   BUTTON_L1

key 311   BUTTON_R1

key 314   BUTTON_SELECT

key 315   BUTTON_START

# Left and right stick.

axis 0x00 X

axis 0x01 Y

axis 0x3 Z

axis 0x4 RZ

# Triggers.

axis 0x5 split 0x00008000 LTRIGGER RTRIGGER

# Hat.

axis 0x10 HAT_X

axis 0x11 HAT_Y

 Now after a reconnect of the device everything should work as intended except for pressing the Analog sticks (They don't send any signal in HID mode) and pressing both triggers at the same time since they are interpreted as one axis. And after trying for hours to find the right split value for it just by trying hundreds of different ones, I don't have the energy or knowledge left to fix it.