I have no experience with this stuff but i did scan the weblink you sent. I saw absolutely nothing about the thermal properties of this material.
The perlite is used as an insulator, very small amount is used and it is inexpensive. It is non reactive so I really do not see the advantage of substituting a material which apparently is reactive in many circumstances, personally, i could not name all the possible byproducts of burning
wood or whatever else you might burn (say an envelope to start the stove).
If you would like to experiment with this product, I would choose to use it in some place where it is easier to change your mind about it than the core of a
rmh. It sounds like there is many useful applications. Please use natural product.
Just my humble opinion