This discussion is missing one important point from each poster.
What head are you using in the Demi ?
Bare tube, covered tube, clear or white if covered ?
It makes a significant difference.
I have one of the original Mola Demis and a brand new one. The reflectors are identical but the original has an opal glass that is 1.25 inches in diameter larger, 8.25", than the current ones which are 7". My new Demi has the PAD, or perforated aluminum disk.
Guess which one is more even from center to edge and has lower contrast overall ?
Yes, you guessed it. It depends on the head you use.
The Demi with the PAD and a Profoto Pro 7 head, with the standard white glass envelope over the tube, is very even from edge to edge and provides the classic Mola beauty light look. The older Demi with the opal glass works well with an Elinchrom Ranger S head. The shorter, more recessed circular Elinchrom tube disperses more lateral light and sits further back from the opal glass. It's much more even than with the PF Pro 7 head behind the opal glass. These respective combinations are very close to each other, but that opal glass is always hotter in the center.
The PAD was developed as a more durable / less breakable diffusor for the Molas so that they're easier to travel with. Then someone stacked them and liked the results. Mola took that idea and ran with it. Now they can sell you both. I've tried it. It has a negligible effect in my opinion. And I've tried it with Broncolor, Profoto, Comet, Dynalite, Elinchrom and Norman heads.
Funny isn't it. You look at the opal glass and PAD and just immediately assume the glass is going to create a more even light. it doesn't.