I've had the Nüüd for the 5S and the 6.
Notable Improvements:
1. The fingerprint window is bigger and more efficient (granted the 6S is too but it works much more flawless than in the past)
2. The bezel for swiping up and down menus is much better. Not even an issue anymore.
3. Sound quality both speaking and listening is better.
4. Ear hair doesn't catch the window anymore
5. The adapter for non iPhone buds is smaller and flat wired.
Issues:
1. The charge door is pretty rough to open and close. This may just be because it is new. More to follow.
Will check out the speaker system tomorrow.
Definitely has a better look and finish than the 6 model. Same style, just feels refined.