Carb. Tuning with Cylinder Shorting Tach/Dwell

I have never seen any comments on this board but has anyone ever used a Cylinder Shorting Tach/Dwell to adjust the carburetor A/F mixture? There is a simple three wire hookup and then you program in the # of cylinders, firing order, and cycles. Then each individual cylinder is shorted out and it measures the rpm drop and also the % contribution of each cylinder to the total cylinders. The cylinders with the lowest % contribution or rpm drop are the ones that need attention (maybe A/F tweaked). One problem though when there are two distributors you need to program 4 cylinders rather than 8 and when determining % contribution it has to be based on 8 cylinders. Anyone have any experience, comments, or opinions??