The A Ball Set is meant primarily for use with the 2" RAT. You will see that if you are using a large ball, the 1.550" tool works better than when you are using small balls - just as small balls work better when used with the strongest magnet. The larger the ball, the more pull you are going to have to it by a smaller magnet. The small the ball, the more it is going to be attracted to a larger magnet. Again, keeping in mind that MDRS results are dependent upon the thickness and tensile strength of the brass with which you are working, we've experienced great results using the A Ball Set in conjunction with the 2" RAT on smaller tubing: Baritone and euphonium branches, marching brass, German tuba tuning slides, etc.
Remember, just because the MDRS does not work miraculously on every instrument, the instruments that it does work on makes it all worth while.