Although the above "Tuner Test" is testing shooting with different weights on a barrel it isn't a true Tuner. Tuners work on Center Fire Bench rest guns and you can most definitely make groups grow and shrink. You'll actually be able to change the group from round, to horizontal, to vertical from big to small. That will all happen in a half of a turn of the tuner. Now, one thing a tuner won't do is fix a barrel or load that doesn't work.
Tuners also work on factory guns; the results just wont be as noticeable. It's the same thing as the Browning Boss, which is a tuner/brake or just a plain tuner.