Cons would be cool just be aware you need some good sight breaks if you plan on stocking any tank mates with a breeding pair in a tank that small. Stick with something like a pleco. Also be wary of the amount of beppies... You will need a fry disposal unit haha. (The pleco will gobble eggs at least.)
Also a community of livebearers would do good in a heavily planted 40b. Larger swordtails would be cool.