I use a RCBS uniflow and usually load 50 rounds at a time. Every time I have checked for uniformity with Unique it varied approx .2 tenths. I use it in .357, .44, and 45 colt. It doesn't seem to affect my 25 yd groups. [maybe if I used a mechanical pistol rest there would be a difference]
Am thinking dhom nailed it. People assume the slight variations in charge weights you may get with unique and some powder measures equal a variation in accuracy. Like automatically assuming a lesser ES in small number of velocity readings equates to better accuracy, it just ain't so.