We just loved our hens- but only had four at a time, in a very large garden- so they didn't smell. The grass in the pen went quickly- but most of the time they had access to the whole of the back garden, about 1/3rd of an acre. They never caused trouble in the borders, and they didn't have access to the veg plot- they would jump and get the apples from the bottom run of the espaliers apples, and that was fine. In a small garden, if kept in a pen, they would get smelly, unless you can move their pen around to let grass re-grow. We used to have moss in the grass before we had them, but it all went.
All different characters and personalities- it was fab. Would love some here, but too many foxes, beech and pine martens- it would be a constant battle. I do miss them though.