The cast marble feels great, heavy and shiny and smooth... and I still haven't solved it. I thought I knew how it would open, but after reading some comments, I'm not sure anymore.
The nutcase, I have to say disappointed me a little. It's rated at grade 6, but I solved it in 5 minutes. And 5 minutes later I had it assembled back in both versions (nutcase and casenut). So it seemed very easy to me. And the "feel" isn't great, it feels "cheap"... not tight enough, the movements are not smooth, and it's a bit too light!

That said, my wife still hasn't figured it out, so maybe I just lucked out in understanding how it works...
Cristian