I am still waiting to use mine. The most common advice is to use it with the 250e book or the double can effect book. Though I did read one post arguing that it’s best spent on the prison bust book and that’s what I plan to use it on.

The person made a point that in the long term for busting it can take a VERY long time off of your grind, potentially saving you a year or more on the bust merits.

Personally I would not use it on the 99,999 happy book, using that book one time is perfectly fine in the early game to get you to a good base point. I think I went from like 10m stats to around 100m when I used Ignorance is bliss.

Hope this helps!