We use them in our indoor plants, we put them on top of the soil. They dry up and have to be soaked, we have been pulling them out and soaking them. I would not use them alone as they have none of the stuff plants need. But they do work Ok.
The things I do are an evolution and I am always learning. My way is not the only way of doing things, and I may and will change the way I do things as I learn better ways. So any advice that I give is in that spirit.