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.