First off - those look like nice plants. The roots look very good from what I can see in the picture.

I've been on this lava rock kick since early this spring. I've moved almost all of my Dends to it. So far, they seem the happiest I've ever seen them. Despite being a very careful waterer, I've always had problems with bad root on these things when I grew them in bark. That problem seems to be solved now.