I can understand where The Mad Collector is coming from, ive seen plenty of merch that fits the "rip off" description but i can't say it applies to the new book personally.
1. Not everyone is able to afford all the diaries.
2. it's a 4 for 1 deal.
3. The diaries aren't in print any more so you could simply take this as them being in print again.
4. Isn't all merch a "money making scheme"? What matters is whether you think it's worth your money or not. For Mad it isn't but i don't think that makes it a bad thing.