If they are what I think they are they have been around awhile and are often found in commercial potting mixes labeled for extra water retention. As far as I am concerned the jury is out in terms of whether they work as advertised or not. I have heard from folks I trust that some do, but years ago I had a mix with them in it (couldn't tell you the brand) and it sat in the shed, open and dried to the bone. When I looked at it those crystals were still fat and plump which told me it didn't release the water to the mix.

If it doesn't release it to the mix I am not real confident the roots could pull the water away from or out of it either.