This is just concerning the 19 mm pads, not the original OD flow groove, the original flow groove is great. If you look in the description of the 19 mm pads, it says that they are thinner than normal 19 mm slim pads which makes them very slippy. In a YYF nightmare these pads are really slippy, I haven't put them into any other yoyos because of how slippy these are. These would probably work better in a yoyo with a narrower gap, maybe somewhere around 4.5 mm as opposed to the 5 mm in the nightmare. I'm not saying that these are poorly made. They just don't work for every yoyo.