I only started using Affinity at the start of the Designer Windows beta, but have since purchased both Designer and Photo, though I've still not spent much time in Photo yet....
The main reason being I've been using gimp for many years and there are a couple things that either Affinity isnt able to do, takes much longer or I've not figured out how to yet.
Mostly my issue is with aligning, in Gimp I've been using this script https://chiselapp.com/user/saulgoode/repository/script-fu/wiki?name=sg-fit-facewhich isnt a lot of code, but allows me to pick two points on one layer, and two points on another layer and it rotates and scales one to fit the other flawlessly!
The other thing keeping me in Gimp more than I'd like (I really want to migrate completely to Affinity but it's not happening as smoothly as I'd hoped!) is the simple "Colour to Alpha" option in Gimp, which in a couple clicks removes a white paper background from a drawing, without messy edges, which is something I've only manage to (not perfectly) replicate with endless selection-refine-feather-refine-select-mask-cut-blur, and it doesnt get me the same results, despite taking ages.