The Accura MR is a solid rifle. Personally, I like the MR stock configuration over the standard Accura stock. It should serve you well.
As for Blackhorn....when compared to Pyrodex, it's a bit hotter, less corrosive and the fouling is a much finer fouling which makes loading a second shot much easier. When compared to Triple 7, velocities are pretty similar but Blackhorn starts to gain an edge in velocity when the bullet weight starts going up. One of the biggest reasons folks tend to like Blackhorn over Triple 7 is the lack of the dreaded crud ring formation and ease of loading with consecutive shots. Ease of cleaning is subjective. I don't find that Blackhorn cleans up any easier than other BP substitutes. Blackhorn requires solvent cleaners such as Hoppes as where Triple 7 and Pyrodex can be effectively cleaned with soapy water, Windex, etc.....so pick your poison when it comes to cleaning.