We have sold quite few of our precision barrel bushings. We have had numerous reports of accuracy improvements. Some dramatic, some not as dramatic. The factory CZ barrel bushing is hand ground at the factory to achieve the necessary clearance to allow the barrel to install in the slide. If you have one fitted well, the accuracy improvement with a precision bushing may not be significant.
However, in many cases the bushing can be quite loose, as much as .006" at lock up. Ideally at lock up there should be .001" of clearance or less. We have documentation of groups at 50 yards from a standard CZ75B going from 6" to 1 and 5/8". Many CZ's with the precision barrel bushing will shoot quarter sized clusters at 20-25 yards from a rest with good ammo.