Hi Pants. I have tried a few orchids in it. Have not done any real scientific studies like Ray has, but here's my
Pros:
Does not float at all which, for me, makes it easier to wash. This adds to stability of plant in the pot compared to Hydroton.
Cons:
Much more expensive than most other media. Promotes algae growth much faster than other medias. Much heavier than any of the LECAs.
General Comments:
Ray, I agree with your statement about uniform particles allowing greater air penetration, but in a side by side comparison of 8 Zygo seedlings, half in Hygromite and half in Hydroton, there is no apparent advantage of the Hygromite over the Hydroton. It does appear to wick water a little higher and I think that accounts for the excessive algae growth on top of the medium. I do use it sometimes to kind of "top off" plants in Hydroton and this kind of helps keep me from blasting the marbles (my wifes term for the Hydroton) out of the pot when watering.