I read about this substrate mix (also, @LeatherSolis uses it whose plants look amazing!) so I've decided to try it, too. Don't get me wrong, I love pumice and I'll keep using it, but I just need to satisfy my curiosity.
Both Akadama and Kanuma substrates are mostly used for bonsai in these parts of the world. Apparently in Japan it's beeing used a lot for mesembs, too. The qualities of both substrates seem to be similar to pumice. Akadama (brown) is slightly acidic, Kanuma (yellow) - more. I'm going to try it with a couple of adult plants as well as for sowing (more Akadama, less Kanuma, maybe with some vermiculite mixed in) and report on my observations.