I have 2 ferrets..
Cons: They smell, even descented ones smell. Bathing helps but too much bathing makes it worse because their oils overproduce if dried out so they smell MORE! Things can be added to their water to help reduce smell but they will always have that musky scent. Fish based foods make them stink more so I stick to chicken based ones. Their poop stinks...they can be littertrained but they will go in any corner if a litter box isnt handy.
They need out of cage time..everyday. They are not cage animals happy in a cage, they are smart, inquisitive animals that need stimulation and your time. They tend to be nippy as babies. You can teach them not to nip, but even adults can and will bite. They bite hard too, even when just playing. They have thick skins and mostly aren't trying to hurt you, just play. But their play is very tough.
They are touch on cage accessories. Mine have ripped up so many hammocks and tunnels. Its crazy. They are prone to lymphoma and other problems. They have a short digestive tract so they poop a lot and if they swallow something bad, it can kill them easily. They can fit through any opening the size of their skull so FERRETPROOF their area.
Pros: SO funny. They crack me up. They are so fun to play with and mess with. I stick mine into a used sock...oh they love it! They love to tunnel and "ferret" their way through obstacles. They have a decent lifespan so they are a family member (unlike rodents that die so soon). They can be littertrained, leash trained, and shoulder trained. They can even learn tricks. My albino female stands on command for treats. They sleep a lot so when you are not home, don't worry. As long as you play with them later they are a-ok with it (unlike, say a puppy)
Hope that helps. If you want to know anything else, just ask!