To put it bluntly, I hate hexagon tanks. They are more form over function, appealing to humans (well some... I don't like the shape), and not the fish. Oxygen content and gas exchange is low on a hex, they are deeper than wide. There is little room for the fish to swim; fish generally do not swim up and down. They are hard to clean. I wouldn't get a hex. You are being offered a used tank cheaply, go for it if you want. But I wouldn't suggest them for anyone looking for a new tank, a flat back hex would be fine, just not a regular one.