To me it sounds as though the spheres are replacements for bio balls. If you use bioballs, maybe a good product.
The rock/blocks are replacements for live rock. If you prefer to not use rock, probably a good alternative.
If you have a reef with rock and no bioballs, I'm not sure they have a purpose?
I could see the blocks being good for those that want a very minimal rock scape where you could toss a couple in the sump.
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Brad
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