Our three VIADUKT mainly differ in their size and what you can fit in there.
The VIADUKT is for us the perfect bag for a weekend stroll, whereas the VIADUKT DAY is perfect for a day at the office with not too many other essentials. The VIADUKT WORK is perfect when you want to fit all your essentials into the bag (or are on a work trip).
Smaller differences are that the VIADUKT has a zipper pocket inside instead of a laptop compartment, whereas the other two bags have a zipper at the bag and metal feet at the bottom. The volume of the VIADUKT and VIADUKT DAY can both be adjusted by regulating the strap at the top of the bag.