Beats me. I was advised to use it when I started, earlier this year, by a couple of our local club members, and it's been working fine. I've got some 1st year maples in it, along with my zelkiva, a chinese elm, a flowering quince, two dwarf youpons and a pride of Houston holly, and they're all thriving. As in most things, however, you must be the judge of what works for you.
On a related subject, I just read an interesting article on the
Knowledge of Bonsai website titled
The Secret to Soil Revealed! which makes a lot of sense to me from a "common sense" standpoint.
Based on this article and the amount of care that you're willing to give your trees, I don't see that it would matter that much. But I'm still a beginner, and probably will be for years to come.
