Ease of use. That's what's happening with this cap and hard rubber roller combo.
We've used foam brushes, paint brushes, squeeze bottles, rollers, even fingers with Inkodye, and here Lumi comes along and crashes our messy party with a quick, clean, neat way of applying their dye! The nerve!
Jokes aside, this contraption comes in quite handy when you happen to be dealing with a thin, flow-able paint or dye that needs to be applied to a large area, stat! There's even a little stopper on the back of the roller so you can put the pause button on if the dye or paint starts to get out of control.
The roller fits Inkodye bottles, as well as any bottle with a standard 24/410 cap.