Oh how cool, I've just repotted my maple bonsai-candidate, and I put it in pretty much that mix. I used Turface, pine bark fines, and "chick grit" that's just a little smaller than that lava rock (it's the "gritty mix" recipe from Tapla over on DG, although I didn't take the extra step of screening the tiny bits out of the pine bark).
I bought a new (green leaf) J Maple baby at a plant sale last weekend... deliberately chose the one with the twisty trunk.
