Of my 3 uniflows, I find that each one has a different wear pattern so they behave differently. My small pistol one with the small micrometer cylinder and insert is heavily worn and very smooth. It will throw bullseye (5.0 grns) spot on time after time with the occasional 4.9 grns. I normally set it up so the load is a hair light but hits the desired amount most of the time and goes light rarely.
My rifle uniflow on the other hand does not do pistol powders well but is good at big charges (40 to 80 grns) because that is what I run though it the most.
My third uniflow is brand new. It has only seen a few thousand grains of powder through it and it is not consistent, not smooth at all. Either RCBS is just making them rougher or I have forgotten how they were new. Either way, I am sure it will wear in as I use it more.
The key is to use a baffle, keep the powder reservoir full and consistency. You have to just experiment and develop your own technique for accuracy.
10mm and 357sig, the best things to come along since the 38 super!