I believe, originally, Midwest was going to make cages specific for all types of small animals: chinchillas, rats, sugar gliders, etc. However, the price of metal went up drastically and the cost of producing numerous different cages became unfeasible. So, they compromised, put out the Critter Nation which is supposed to be suitable for all small animals, with the smaller bar spacing that the rat and glider owners wanted. Last I heard, they were going to market critter specific modification packs - i.e. a Chinchilla pack to go with the Critter Nation that had additional ledges and such, a Rat pack, etc. I haven't heard anything more on this in quite a while, and my guess is the Critter Nation, as it is, is the final product. It is nice for rat owners, who previously had to wrap the FNs with wire mesh to keep rats from fitting through the bars, but the FN size and bar spacing is suitable for adolescent and adult chins as is.
The Critter Nation's bar spacing, while smaller, it's still not baby safe.
The one thing I do like about the CN for chins versus the FN is that the bars are horizontal instead of vertical, giving you more options to place ledges, shelves, hammocks, etc.