I'm semi-pleased with the result. I love the effect, but there are some imperfections that are going to annoy me, like the diagonal lines not being straight and the fact that the topcoat slightly smudged some of the dots. I'm pleased that the dots look reasonably even as this is what I thought I would have the most problem with!
Here's a step-by-step photo guide to how I did this. Masking tape to create the divide, and a dotting tool for the spots! (Oh - and the black nail art pen also has a brush, so I used this as it's the only black I have!)