I have a cheap snaredrum that has a rather ugly ringing sound. I prefer a fairly dry snare sound, and the Evans E-ring fixes that problem perfectly.
I actually bought both the 1" and the 2" ring, so I can adjust how much dampening I get, which works very well.
It doesn't require any attachment, just drop it on the drum head, the rim of the drum keeps it in place. It takes 2 seconds to put on or to remove it.
Other than that, it is obviously a very simple product, it's plastic, it's solid, so I guess it is a very simple product to make.
But it also costs next to nothing, so I'm very happy with both my E-rings.