Since there is so much negativity and lack of understanding of the Di2 system for mountain bikes, as a proud owner of the Di2 on my enduro rig, and soon to be on my new hard tail, I would like to converse with other owners, soon to be owners, or those who want to know more before they commit to buy. Do not knock tech until you have tried it!
All electric cables run internally, with very little exposed except for a few inches to connect to the rear mech out of the back of the chainstay, small section from the BB to the chainstay, and from the front of the downtube to the display.