Ive grown lucky bamboo in it successfully but that's it... When I get more plants I'll experiment with it some more and see if it would be a solution. The problem I had is that somehow it had a really bad algae problem in the middle somehow...
These balls change their diameter very much while taking and leaking water.
They are not intended for growing plants, but to decorate cut flowers in a big glass, so that the stalks of the flowers are a bit stabilised and don't fall to the side.
The only nutrients your plants will have in this "soil" is from the water you soak them in.
I once tried to keep carnivorous plants in a kind of "flask garden", closed and sealed system with a white 1W highpower LED for lighting and I used such crystal balls at the bottom of the container, as a water-keeping and drainage layer, above pure peat and speperated by a garden fleece. But it didn't work on the long run, because the living Spagnum in the container grew too much: After twelve months of that closed flask garden, all carnivorous plants were overgrown by Sphagnum, which filled the container nearly completely.
Perhaps you can soak the crystal balls in rain water, fill them into a glass and keep some wet-loving Utrics in it? That's something I wanted to try one day.
There's a thread about this on CPUK, but you can't get them in the UK (I don't think, anyway) - so no-one has tried using them. I guess the main problem is keeping them hydrated. People have suggested soaking them in their pot every now and then to keep the water stocked in them high. As long as there are no added fertilisers, it COULD work- maybe more so for things like utrics. I can ima imagine problems with lack of acidity with some plants like VFTs etc. Someone should still give them a go though, IMO.