I've seen these on there. I actually contemplated purchasing some. Unfortunately it's hard with dry rock to increase biodiversity in your tank without shelling out big bucks on websites like this. Same thing as the coralline in a bottle, bristle worms from IPSF, etc.
Would be nice if we had a sticky thread on the forums of established tank owners willing to ship stuff like this to new people. Could be an extension of the Reefers Code of sharing grown out frags with newbies for a reasonable price.
Imagine if everyone with a successful tank on here stuck a few marcos rocks in there sump for 6-12 months and mailed them to people to seed tanks. They would be covered with coralline, pods, asterinas, sponges, etc. I think the lack of live rock availability wouldn't really be a problem anymore.
I think all these hitchhikers and various forms of life help to establish a stable tank, but unfortunately with dry rock you get nothing. Not to mention the recommendations for dipping corals likely takes off the bulk of good hitchhikers as well.
One of my favorite parts of my old tank years ago (live rock) was discovering new hitchhikers in the tank. (Asterinas, Bristleworms, pineapple sponges, coralline, etc.)