I live in a small inner-city apartment. I am lucky to have a small courtyard area with a modest garden. I was thinking about getting a worm farm but am worried about the smell. Obviously, up close they would stink a bit, but could this permeate the entire court yard area (5m X 5m) making it uncomfortable to use?
I have one, and I would have to say it's possible but not certain that it will smell. With care you could avoid it as demonstrated by people using them indoors. You would have to be more careful than me about the amount of water that gets in, and possibly about the mix of food hot give them. Mine has a sump to collect liquid plant food, and a tap to remove it, but doesn't drain completely and some scraps fall through into that and decompose anaerobically, which sometimes smells (the smell is distinctive, different to rotting food).
I've seen smaller designs that should drain completely, with a tap under the middle of a funnel-shaped sump. these would probably be more suitable for you. Also I live in a rather wet climate so rain gets in the vent holes.
If you run your worm farm properly then it doesn't smell. It will give of a earthy scent. However if things go wrong because your worm farm contains too much water or nitrogen then it will start to smell sour or rotten. So make sure you have proper drainage and keep an eye on the C:N ratio of whatever you put in the farm.
If you are using your worms to process food leftovers and want to be on the safe side regarding smells, you can bury food under already processed compost. Also make sure mice, rats and other rodents don't have access to the heap.
For what it's worth; I have my own worm farm in a small container in our shed and I never had any problems with bad smells or vermin, but I am somewhat selective of what I feed my worms (no meat, dairy or oily foods).