I didn't like it at all. It was my first "tank" I bought when I first got Pisces. Only had it for a day or two before I returned it and bought a 2.5 gallon (which is now home to my little female Lucy). Pisces let me know that it was way to small, he even threw a fit when he was upgraded to a 2.5, didn't think it was enough space! Once I got him his five gallon he was perfectly happy. Spent a fortune on all the upgrades though...Oh well, at least he's happy!
In my opinion, it is way too tiny, Pisces was absolutely miserable in it and he kept trying to attack the yin-yang fish. You can add a heater (there is one by marina that would work) but, I wouldn't bother you would be better off in the long run just buying a 2.5 gallon with a heater. Your fish will definitely be healthier if you go with the 2.5 gallon. In fact, I actually wrote a review for that particular tank. You can probably figure out which review is mine. Haha.