I think I have mentioned before, the family of our New Zealand Daughter-in Law's sister, who have lived in the Newcastle area of the UK for many years, from a time when the two son's, now in their twenties, were quite small. It always amuses me, when we get together to hear Mum and Dad, still with a noticeable New Zealand accent, and the two sons who are broad Geordie.
This looks excellent and will work well I am sure,.....till you decide you want to move it or modify it when you will breaking up concrete (I know I have been there).
I now use something called grano in the UK which is basically 5mm to dust granite chippings (quite like chicken grit but with more dust). This locks together just like real ballast allows for some track expansion and movement and can be easily topped up and modified. It is laid on a polyethene sheet to keep the weeds out. The main down side is it needs to be wider than the system used here and needs topping up annually, but is very quick to lay down (dig the trench put done the polyethene fill with grano tamp down and lay the track. I am now on my 5th ton of grano (over a decade).