We have a ferret Nation cage model 124 at our house. It houses my sisters 3 adoreable little ferrets usually but my little girl has recently moved in temporarily. It is an amazing cage, I would love to get one for my ferret someday. That's kind of my goal at the moment.
The cages roll which is really nice and the cage itself honestly isn't that heavy. The wheels move smoothly even on old hard wood floors. There is a nice sized storage place underneath perfect for all the collars, harnesses, leashes, shampoo, treats, extra fleece and all those many ferret toys. There is room enough to seperate them all into their own little shelves or buckets even.
The cage is very roomy with 2 adjustable shelves and ramps. It has two double doors on top and bottom with dual locking latches on each set. We have enough room for a hammock, random fleece, two sleeping bags, a dry bathtub (they like to sleep in, tent, food, two water bottles and there is still room for probably another one or two ferrets. The ferrets don't have to be around each other if they don't want to be.
Even the single units are pretty big honestly for housing maybe 2 ferrets. These cages are also good for other small animals like rats or Chinnichillas. I've never seen anything bad about these cages anywhere I can honestly say it is probably the perfect home for any little critters.