Uni Posca PC-1MR Marker White Ultra Fine 0.7mm Tip Nib

These are my least favourite of the Posca white range of markers. I'm a devotee of the brand and of their white markers, but this ultra-fine point one has been quite a disappointment. I bought these markers at a good price to use them in my mixed media projects to write and draw on acrylic paint. Like any other Posca marker, I have to pump it out the first time I use it for the ink to flow out. However, unlike the other white Posca markers, whose nibs retain ink for while and you have to re-pump them once in a while, these ones don't retain ink in the nib, so the ink doesn't flow naturally and I have to pump them out or shake them continuously. What's worse, the quality and saturation of the lines are deficient. Just frustrating. I won't be buying this finer point nib again.