Ingredients aren't really packaged for brewing small volumes, so you'll end up wasting a lot of yeast and hops. If you use dry yeast and brew frequently it will be fine, and repitching from batch to batch will help. For the hops, investing in a vacuum sealer will solve the problem.
Those are the biggest issues I see, and they're pretty small. I've never done a 6-pack, but I've done some 1-gallon batches. It's great, I recommend it.