I haven't seen a Popit up close and personal, but in the video from the Ys site, it looks like it has a little tab on the free edge, to use for leverage when you pinch it off the enhancement. The ENUKs don't have that, as they are meant to stay on the nail.
When you see the videos of the enuk inverted molds and other inverted molds you will notice that a lot of product seeps out around the edges,
the pop its are unique in that they have a skirt around the edges so you don't get any seepage provided you have the correct mix ratio, have not put too much product into the pop it and do not apply too much pressure,
and they do not produce ugly flat nails like the inverted molds, they have a beautiful vertical apex that gives a perfect line of light hth