I needed more channels and more flexibility in terms of which fader controls which input/output channel, group or DCA.
The QU-5D can do this since it has 38 channels vs 18 on the QU-16. Also it has four custom layers instead of one! This makes it really flexible.
I like the fact that the RTA is under the PEQ instead of a separate feature.
The firmware interface is really easy to navigate around, everything is where you expect it to be. It feels very modern and well laid out. Processing is also easier to control thanks to it larger screen size (almost 2 times bigger, thanks to being 2 inch diagonally larger).
Also the console sounds better to my ears.
I really recommend this product to anyone looking to upgrade form the QU-16 or, if you currently have an other brand and looking for better quality and usability :)