No experience with Calcium Montmorillonite clay but Soilmaster is fired montmorillonite clay and I believe Turface products are too, maybe even Flourite. All are pretty good substrates for planted tanks.
How do you plan on using this? It seems fairly expensive in comparison to something like CSM+B or some of the other micro fertilizer supplements out there but may last longer since it will be used in the substrate. I'd rather be able to control the addition of a liquid fertilizer than risk having the clay particles cloud my water. I've been down that road before
Yes, I've been trading emails with Aaron about this. I was concerned that it doesn't quite meet the mineralized clay recipe. However, the red clay in the recipe, I believe, was for adding iron to the substrate and I have the Flourite to do that. So, I'm thinking that the montmorillonite should work okay. I'm still soaking the topsoil so I will be a few more days before the tank is setup. I'll let you know how it goes!