I recently got one. I'm not convinced it's that great.
Does it make an unmuffled drum sound better? Sure, because it effectively muffles the reso. Does it sound better than a muffled drum? I actually switched back and forth between the kick port with no muffling on the reso and no kick port with an evans eq pad on the reso. I thought the sounds were almost identical. The kick port had a slight edge because I felt the drum had a little more volume.
I don't think there is that much magic going on with this thing. What I do think it does is to muffle the reso head without having to take up any space in the drum with towels/pillows/pads/etc. So what you end up with is a nice muffled sound but you don't lose the volume you would with the towels/pillows/pads/etc.
I'm not convinced you couldn't get the same or better sound with good head choice. In fact I'm going to be switching over to an Aquarian Superkick II and an Aquarian regulator reso head to see if I can achieve a similar (or hopefully better) sound with no muffling in the drum.
The bottom line is if mine was stolen today I probably wouldn't buy another one.