I think the only thing lacking within Margin note is the ability to start notes than run towards the left. As a visual person, this would be massively advantageous. I also think you should be able to add notes to corners and in different positions of your choice onto the individual boxes.
I am dyslexic, so for me the visual aspects are extremely important. Everything else about this app, is phenomenal. It is quite literally changing my life it’s that good.