The science is pretty simple. Don't take the energy of sub into the floor. That creates a kind of resonance and hence boominess. You can feel the energy transmitted in your seat as well. Many wrongly think that as a great bass. For reference, check any imax theatres

. I have IsoAcoustics L8R200 for my 2.1 setup. I love it. In my HT room, i have used a 2" thick foam that came with one of the packing material. That does the job as well. There is no doubt the L8R200 is aesthetically much better. I wouldn't hesitate again to get one just for aesthetics. Also, it is easier to clean the area without moving things. I am using ISO-L8R130 along with my Neumann KH120 monitors. Again, it causes a huge difference.
If you have a down firing sub, i would still recommend to have some space between port and floor. It is not ideal to cover the port completely with a mat/sponge.