Mark, a tune made my Disco much smoother to cock the bolt and load pellets, simple crown job improved accuracy. Also filed down transfer port, which comes too high from the factory sometimes. Did all the work myself, as I usually do... Do not know about the muzzle brakes, I am using Anthony Storey one, works very well.
Power adjuster can be added as well to get more consistent shots. I do not have one.
Disco is a good rifle to work with, replacement parts are available cheap from Crosman.
Chris