I got mine too.
The standard foam is 45 density, the middle 65 and the top 100.
The 100 is too dense and has little compressibility. I think it would be useful for monster tanks, or I'd use their hybrid foam. I don't think the cost is justified for smaller tanks.
If you wanted only 0.5 cm thickness I'd go with the 65 foam, but I think with a big tank it could bottom out at 0.5..
To compare I then stacked the two sheets of 45 from the trial pack so I had a 10mm 45 and 10mm 65. I couldn't really tell the difference between 45 and 65. I certainly can't compress a 1cm thickness of either to collapse. Both are flexible and should compress to give a smooth top ironing out but not transmitting high spots. Not that there are any in the stand as far as I can tell. Both absorb point pressure well but don't deform much with my whole body weight on it, both 45 and 65 are easy to cut with a standard knife. I'm putting a 400l tank on it and just ordered the 45, I hope it's the right choice!
I'll post the tests that I did later in full.
But I sat a 10x10cm square of wood on the foam and stood on it on one leg, that's about 75kg going through 10cm with no collapse on either foam. For point pressure I used a pen point to equate to a grain of sand under a tank, all foams absorbed it, the least dense the most quickly but damaged the most.
Even the standard craft foam is the same density as high impact gym mats etc....