Draw backs are pretty limited in a Nano. The main problem with a nano is space (inside the tank)! The other thing to consider is water quality. Since you are dealing with such a small amount of water specs can fluxuate quite a bit if your not careful. But your not new to this game so you should be fine. Check into a Nanocube 12DX by JBJ. The best tank of it's size out there IMO. They also make a 6 and a 24 gallon.
Bob