Update:

5 out of 7 Kobo purchases tracked and are showing the 250 bonus as 'pending'.

The 2 that didn't track were the ones where I was lazy and didn't change the country to Ireland after clicking through the affiliate link from eStore. It seems being logged in to an Irish account isn't enough even if you get billed in Euros.

2 of the purchases that tracked were for €0.49 and are showing 1 point plus 250 bonus.

Also, it appears the 250 bonus points offer has now been extended until 25th April so should be able to get some good mileage out of this.