READ THE DESCRIPTION BEFORE YOU BUY TO MAKE SURE YOU ARE GETTING THE RIGHT NIB FOR THE RIGHT MARKER. These are great. I use these for drawing on paper (figurative & landscape drawing, not graf) with a Molotow dripstick. Even on smooth surfaces, the felt eventually wears away and needs replacement, which is why I'm glad that these come in a five-pack. Using them on canvas or rough paper will shred them much faster, so I try to avoid it but you gotta do what you gotta do. My most recent favorite paper is Color-Aid, which is painted paper that has a fine sandpaper-like texture. I only use the dripstick on it minimally and try to not press down at all, but it still pulls the felt off pretty fast. All that being said, these are STILL great. Always buy the five pack.
If you want to be able to just unscrew to refill without removing a valve, this is for you. That's it. That's all it does. Is it it worth it? In my opinion hell yes.
I started using Molotov 127's to do highlights on my illustrations. I liked that they are refillable and have interchangeable/replacable nibs. But my very first time doing a refill, I accidentally separated the valve and had the spring fly out and basically destroyed it.
Since then I've mastered removing that valve, but when I use these on my markers it's not even a concern. I don't have to find a spot to put the ink-covered valve down on. I don't even get ink on my hands. Yes the ink will wash off but constantly washing my hands leads to f*cking up my skin. So for my uses, these are great.