This is a very quirky and fun publication, with some strong themes for subclasses and an intriguing adventure (I haven't run it yet). Given it's for charity, I would encourage anyone to grab a copy, although there would be a good argument for buying it anyway, even if that wasn't the case.
However, I would like to highlight a few things to the writers which it would be nice to see ammended.
The only significant issue is that quite a few of the subclass features are unclear (the ranger beast collector's "The Secret to Training Success" is particularly problematic). Having discussed with DM friends and looked back at a few old books, I get the impression that several of the subclasses were originally designed for a previous edition (3.5e comes to my mind, but I'm unfamiliar with 4e), and have not been fully converted to 5e. There are references to features and mechanics that don't appear in 5e which are essential to understanding a couple of the subclasses - nothing that a DM and a player couldn't puzzle out for themselves, but just might take a fair bit of effort and balancing in a few cases.
I would also suggest looking at phrasing and capitalisation - these are a bit inconstant and don't adopt Wizards' normal grammar and lexis. This rarely obscures meaning, but a bit of polishing would remove imperfections from what is otherwise a very impressively presented publication.
Obviously, this is an April Fool's release, and isn't meant to be taken seriously, but if the rules could be clarified a little, this could see far more table use than it might in its current form.