Hi Lee,
Pretty much the number 1 reason why I purchased Affinity Photo (Licensed) and downloaded the Beta is that I wanted to be able to water mark my photos inside of Mac Photo App.
Also, I really liked the prospect of how Affinity turns Photos into a better photo editor.
The ability to drag in a Logo PNG file or type words over-top a photo completed the workflow I needed for Photos. I have been using Photoshop, Aperture, and Photos to manage my collections but going back and forth is a pain in the butt.
Since Aperture is discontinued I wanted to use Photos for managing the entire workflow of my personal and not-so-important photos but also use for some professional and blogging editorial uses.
I am testing Lightroom but I love the workflow created between Photos, the five MacPhun Extensions, and the possibility of a full featured Affinity extension. It kind of forms the dream team of easy photo management and sharing with powerful tools.
The biggest things missing from Photos are:
1. Powerful Sharp & Noise tools that work
2. Dodge & Burn tools
3. Watermarking
4. Skin smoothing
5. Teeth whitening
6. A vignette that doesn't suck
7. And focus tools.
*There are more minor ones but the MacPhun extensions cover some of those. Affinity covers the rest and offers fantastic tools too but I wanted to access them within Photos as an extension as a fully contained workflow.
Hope my feedback makes sense.
Have a great day,
Shane