What are the fit differences between the MTB and road bike? Essentially, if the fit is the same, there shouldn't be much difference in the comfort factor.

FWIW, I think bullhorn/cowhorn bars offer the benefits of both types of bars, but only if you don't intend to use the drops on roadbars (which obviously you wouldn't).

The MTB brake-shifter levers can slip on quite easily, and the real benefits for mine, are that the curve is another place to put the hands; it's not sharp and doesn't have any additional hardware; and the horn part is much longer than most bar extensions so there is more room for additional hsnd positions. You can also use them in place of road bars, but fitment of the road shifters/brakes is a little more complicated (but doable).