I got one of those as a "gift" a few years ago, and the one I had held about 3 cups of water ,which isn't much. I kept a plant in it for a while and then the seams started leaking when I watered the plant. It went into the garbage.
One of my friends actually bought about 20 of these and hung them all on the wall next to her bed and put a male betta in each. I must admit it looked really cool but then when you think about it, its really not fair to the fish and its a lot of work to keep everything clean. She ended up selling everything off because some started leaking at the seams and it was just too much of a hassle with taking each off the wall one at a time and cleaning it for the fish.