So, finally got the dice. The "Strong and flexible (white or black) plastic" is, indeed, quite strong. No fear tossing them into a bag of dice. I imagine something like a dozen stacked hardback books dropped on one might deform it... but they are strong enough I don't see a need to be careful with them. They have a slightly rough texture that would take dry brushing very well. They are VERY light, but they do still roll well enough. Some numbers on certain dice (double digit numbers on the 20 sider for example) can be pretty small and you'd need to highlight them with some color (paint, ink, fingernail polish). I'll actually pick up more plastic sets than I thought I would after having some in my hands. The "Thorn" set I bought is slightly smaller than standard game dice, so pay attention to the measurements if you order (i.e. get out a ruler and compare to your existing dice to make sure you're not disappointed.
The skull dice are pretty nice, but I think next time I'd buy them in "Detail" or "Ultra Detail" plastic.
The metal dice are really nice, as I expected they would be. I'll need to "ink" them (apply and wipe off so it fills in the crevasses) and they should look really cool. While they are stainless steel they are not too heavy, meaning they aren't going to dent your table if you roll them vigorously. Again, they are slightly smaller than normal sized gaming dice. They also have a gold'ish look to them rather than a shiny silver. All in all, I am happy with the even give the high cost ($65) but I won't be buying loads of other metal sets. One REALLY cool set of dice I can justify, but multiples? Not so much.