I've never used the type of water well in the picture, but we use a similar device (MONA) at the interiorscaping company I work for, and they are very useful in high light areas.
The water well in the picture is made to be put in the bottom of a container that does not drain. Pay attention to the weight of your container before and after you water, as this will give you a clue later when you're wondering how much water is left in there.

This would probably be better used in a covered site, like a porch, because your plants could drown in the rain!

The MONAs we use at work have a bowl underneath them, and the slotted 'lid' snaps tight over it. There is a tube to pour the water into, and check the water level.
Unfortunately you can't buy them retail.

Never used the polymer, or the soil with the pellets in it. It always kinda reminded me of the gel stuff in my kids' diapers! LOL

*And hello to everyone. I don't get much time on the computer, so mostly just read and "lurk" I guess, but you are all such a wonderful wealth of information, and i love this site!