At a bonsai exhibition someone giving a workshop said that if your trees are not in Akadama, you're not doing bonsai.
According to Walter Pall, it does not matter what you use, as long as it is a
modern substrate
According to Walter Pall:
Akadama "is questionable as a good substrate as it inevitably decomposes, especially when exposed to winter frost. It can become deadly loam in the pot, choking the flow of water and air into the soil. This is especially true for trees which are only rarely repotted, like collected conifers and old bonsai in general"
However, according to others, the decomposing is a good thing:
"Over time, root growth and consistent watering break down akadama particles. As the particles break down and become smaller, their ability to hold water increases. Given enough time, the particles will completely break down until all that is left are tiny pieces of clay.
The breakdown of soil particles is important in the cultivation of bonsai as smaller soil particles promote slower growth. During the refinement stages of bonsai development, slow growth is a primary goal as vigorous shoots can thicken branches and make old trees look young"
Source:
bonsaitonight.com/2016/07/15/all-about-akadama/
However, according to the same article, when Akadama continues to break down and the roots start to fill the pot, drainage can be impeded and this will make it hard to keep the tree healthy. Eventually, it must be repotted.
So I guess it depends. For Leatherback, Akadama doesn't work too well. He has had several frost cycles already and his Akadama decomposes fast.
Living in the same small country, but close to the coast, I have not had such frost cycles yet and it is less of a problem for me.
I do have trees (deciduous) in pure Akadama and they are doing fine. My pines are in a mixture, containing Akadama. My young plants and pre-bonsai are in various soils, several of them containing cheap, baked clay pellets *1)
Now, about soil, the person who has great, healthy trees is the one who is right. Walter Pall does have great and healthy trees, but so do others that have a different opinion.
That's why this will be a never ending discussion. It depends on where you are, how you care for your trees (watering, fertilizing), and the trees you have.
Just use what works for you - and that doesn't have to be Akadama.If you use Akadama, make sure you repot in time (but of course you should always repot in time, regardless of what you use).
*1) Aka cat litter