I'm not sure if what we got in the US (Zoobooks would seem to be the corresponding thing) is a better or worse deal. On the downside, the volumes were just magazine sized, but on the positive, it looks like they were the equivalent of $20-50 for their nine volumes a year.
(Looks like there were/are a total of 60 or so distinct volumes, in a rotation where they release(d) an edited version of the same material every 3-5 years; presumably they expect kids to age out of them before they start hitting duplicates.)