First of all, big fan of Affinity Designer. I've been using it almost totally for a year now. Nearly all of my graphics projects at work outside of animation and video have been completed using Affinity products. Of course, there are a few things that could be made better.
Here is a comparison of Designer's "Expand Stroke" function and Illustrator's "Outline Stroke" function on something as simple as a circle with a stroke. Affinity's nodes are seemingly random with a collection of nodes at the top, while illustrator maintains the minimum number of nodes to create the shape.
It is almost impossible to work with the random collection of nodes that Designer presents when working with basic geometry. I would love if this could be fixed somehow!