Pros: Gentle, excellent broodies, the cocks will help take care of the chicks, and males tend to get along well.
Cons: Hard to breed true for plumage color and shank color; tend to lay eggs as clutches of 8-11 and can't adequately cover all of the eggs due to hen size.
I have raised Nankins since 2002 and they quickly became my favorite bantam breed. They tame very well and get along very well with each other, the hens are great broodies, and a pleasant trait of the cocks is that they have retained the ancestral jungle fowl trait of helping the hen with the chicks! That is, when a brood of chicks is about four weeks old, the hen will go back into lay again and produce another clutch of eggs and set on them. Meanwhile, the cock will take over the care of the older chicks. I have seen this again and again in my flock, with the roo' taking on the role of mama hen, taking the chicks foraging and even letting them hide under his wings while resting. This is a trait worth keeping and breeding for, and I have encouraged it in my flock.
One small issue with Nankins is that the hens tend to lay pretty good sized eggs compared to their body size, and they can lay as many as 11 or 12 eggs per clutch (plus, other hens may "contribute" their own eggs to another hen's clutch), so sometimes the hen can't cover all the eggs. You'll want to divide big clutches up among broodies so they only have 6 or so per hen; otherwise, use an incubator for the extra eggs and return the chicks to their brood hen and the chicks she hatched, as soon as they dry off after hatching. The hen can handle all of the chicks once they are hatched.
The coloration of Nankins is, IMO, the hardest thing to keep true, especially with the hens. Dark penciling of the hen saddle-area feathers and white shanks instead of slate (although white is an accepted standard in the British Nankin set of standards, and also was accepted when an American standard first was drafted, if I recall right), are typical problems to come up in breeding, especially if you're line breeding.
Otherwise, these little guys are just a joy to raise and keep!