This is a rather nice invention. A personal size spiral-bound diary (they come in week on two pages vertical and regular) with a long plastic back-sheet with Filofax spaced holes. You just slot it on the rings. Because the plastic is a bit wider than Filofax refills, the spirals do not catch on your Filofax pages.
Find an 18 months 14/10 2014-19/4 2016 here and and 18 month 14/10 2013-19/4 2015 here
That is so clever. It’s things like these that make me wish I thought of it myself, haha! Maybe I’ll try to modify some of my smaller notebooks to replicate this