nothing wrong with small tanks at all!
nanos can be amazingly hard to maintain and as such a true planted nano is a task for the more experienced aquarists.
the need more maintenance, often can be more expensive as if you really want a real nano that is planted and life like, you need to invest in real good lighting, perfect looking substrate, the perfect plants, and most importantly great filtration.
If i set up a nano for someone it usually has an eheim 2213 running on it, is always rimless and usually has t5's suspended above it.
not a cheap task i must say.
much harder to maintain as there is less water and so more room for error as the concentration of pollutants may be higher in a smaller volume of solution.
plus the visual impact of some nanos are absolutely amazing.