We have both a baby biorb and the 30L biorb, both are in the attic. My wife originally got them for my daughters four goldfish she won at the fair last year. They were upgraded to a larger home last spring. In Sept, I decided to use the 30L and set it up next to my computer. It was nice, stocked it with 6 neon tetras and 2 mollies. They never seemed to get tried of swimming in circles and rather enjoyed it. It wasn't bad, but you will be limited to decorations that you can use. Also, you are limited to the fish you can keep. I wanted some bottom feeders, but the footprint of the tank isn't really that large. Also, the coral rock that you have to use for the base isn't really good for algae eaters. The heater wasn't a problem, just ordered a small heater and the adapter for the biorb to let it suction to a round tank.
Having said that, even though I enjoyed the biorb, I opted to upgrade for a more traditional shape and went with a 55gal bow front. While the biorb is good if you have little room, a more rectangular tank is better for surface area.