Well if you consider the NTII there isnt much difference in them. Both Maple necks and Ebony fretboards. I would say the Horizon is fractionally slimmer profile neck (nearer to a D shape than the MII UC, which is more of a C shape) and the MII UC doesnt change radius much down the neck whereas the Horizon does. Maybe its just my imagination though.
My older Horizon custom (1991) is a slightly deeper neck profile than the NT II. More like a Jackson RR1.