Well if that is the way we are going to be about it! Guess I flunked counting "practise" because I have the DataTool gear indicator on my bike.
Ronnie, Accumen and DataTool both make gear indicators. I've seen both of the instructions and they are sufficient so long as you are the least bit proficient with wiring. IMO it is best not to do if you have any doubts about your resources because you will be interfacing with the ECU.
Both brands operate the same, but the programming is different. Accumen has more of a selection, but I am not sold on the materials they use for some of their products.
Both companies have been developing 'plug and play' harnesses for some bikes. If you are serious about it, give them a call and see if they have a harness for your bike. Otherwise, if you want to try it on your own let us know and we can figure the wires. If it were for an 05-07, I could provide the wire id/colors.