This is a nice feature for UFS... I see the usefulness for cartos for sure. Interesting thing is I took a mil off the end of a 510 atty, put it together without the extender and top/extension piece, just as in the video, and used the SS mouth piece. It went together nicely and works for UFS "small" mode to shorten it up just a bit. I have started taking mine to work a lot w/ GGTS and 18350 to get the smallest setup I could. This piece would allow me to not have to grind a little bit my atty (though it will work without grinding them, just the mouthpiece contacts the atty metal to metal) and allow me to use my SS drip tip, so I can prime drip a bit if I need/want to. I will have to pick one of these up, so my UFS will be complete... I already got ss window and mouthpiece!!!