My 1.5 cents. I have it on a '15 RT and it was part of a package that had other things I did want. I have used it and find that the only time it is nice to have is riding two up to avoid helmet bumping on up shifts. Downshifts are less smooth overall and particularly in the 3>2>1 shifts. I am much smoother down shifting than the computer period. If I am riding frisky I don't use it much on up shifting as it is a bit wonky under full throttle and would never, ever trust it downshifting when stuffing it into a corner.
IMO if you don't have it as delivered I don't really think is worth the cash to install later.
If the good old days were so damn good, why did we bother to invent modern times?