They're usually very smooth on paper. The variations of colors of the Uni Style Fit refills are bright and pretty. I find, however, that the lighter shades of blue are not always smooth and may cut in/on ink while one is writing.
...and I especially love that it's available in 0.28 tip. Writes smoothly. No skips and can be used up to the last drop of ink.
Love the variety of colors. I got size 0.5 tips and use these everyday in my planner.