...you cannot tell from the Android screen what is the state of the Led on the Arduino, in the sense that you don't know what was the last keypress made - on or off. I guess there is no option for feedback from the Arduino board back to the Android device, but it might help to put some marker on the Android screen to indicate the last key pressed. Like a little marker that comes on, separate from the on,off keys.
I will have a look at it when back from holydays
My background is Process Control, in term of strategy, I agree, a feedback from the Arduino is much better
This should be feasible 