Back in the summer of 2011, I was one of the million Potterheads who successfully completed a scavenger hunt and quiz that allowed us to register to Pottermore and test the beta version before it opened to the general public. Back then, it was still an interactive site, and you could go through the books chapter by chapter, collecting potion ingredients, chocolate frog cards, galleons, and other things along the way, as well as duel and brew potions to gain House Points. As you progressed through the site, exclusive and previously unreleased writing was unlocked. I started a re-read to go along with the previously unpublished material, but I only got halfway through book two before I lost interest as the content updates were few and far between.
When, after a major update, the interactive, fun side of Pottermore ceased to exist, they compiled (some) of the exclusive content into three ebooks, exclusively sold on the site. Pottermore Presents is a collection of short writings and thoughts by J. K. Rowling, originally featured on the site, with some new additions. It's perhaps important to note that while Rowling wrote the original snippets, the writing is curated by the Pottermore team, and these were never full-fledged stories, despite what the titles imply, but rather mini-biographies and character sketches.
Short Stories from Hogwarts of Heroism, Hardship and Dangerous Hobbies starts out with the life of McGonagall before nicely tying in to a short chapter on Animagi. This is the most detailed background info on any of the characters that you're going to get in these ebooks, but a lot of it felt gratuitous to me, since it wasn't hinted at anywhere in the books; the bits about her early career and love life didn't feel organic to the canon, to be perfectly honest. We then move on to Remus Lupin, his family background, how he came to be bitten by Fenrir Greyback, and how he subsequently suffered throughout childhood, and how he coped in later life. This chapter also goes on a tangent on lycanthropy and the available methods to keep the condition in check. Most of this chapter felt rooted in the actual books and didn't come from nowhere, which made it, in my eyes, the most well-rounded. The most interesting things about the (main) character vignettes are Rowling's short thoughts after each, like what mythological or historical figures she took inspiration from to make up their names, and the fact that with Lupin, she set out to draw a parallel to the stigma surrounding being HIV positive through his experiences as a werewolf, which is really cool to me. The latter fifth closes out with a short chapter on Trelawney and the practice of "Naming Seers", and one on Silvanus Kettleburn, the Care of Magical Creatures teacher before Hagrid, who was only briefly mentioned in Prisoner of Azkaban.
Short Stories from Hogwarts of Power, Politics and Pesky Poltergeists mostly concerns itself with characters who were seduced by power, and was my least favorite and certainly weakest of the three. We begin with our favorite villain, Dolores Umbridge, and continue on to a short history of every Minister for Magic there's ever been, and the changes Azkaban prison underwent under different leadership. Slughorn's chapter didn't contain much new information, but was instead a summary of the info scattered throughout the books, re-packaged into a timeline. It ties in to a chapter on Potions as a magical subject, and then specifically Polyjuice Potion and freaking cauldrons—this volume was a prime example of what I mean when I said that the coherence of these books divided up by "subject" is flimsy at best.... the collection ends with chapters on Professor Quirrell and, I'm assuming for reasons of title alliteration (?!) Peeves the Poltergeist.
Hogwarts: An Incomplete and Unreliable Guide was probably the most cohesive in the way the tidbits were all tied together, and concerned everything relating to Hogwarts, starting with the journey to get there, the Sorting, the castle and its grounds, a very short chapter on lessons, since most have been covered in the other books, as well as its resident ghosts and portraits, and "secrets", i.e. the Chamber of Secrets and rare magical objects which were housed there, such as the Mirror of Erised, the Pensieve, the Philosopher's Stone, and the Sword of Gryffindor. It also reinforced my strong suspicion that it wasn't Rowling that so royally fucked up Cursed Child, since she quite obviously isn't very fond of Time Turners. Finally, I suppose they wanted to keep the three ebooks somewhat comparable in length, but the bit on Peeves would've fit in this collection much better.
To sum them up... The Cursed Child screenplay was a dumpster fire, while these are, for the most part, if not really interesting, at least inoffensive. They could've easily been collected into one larger volume (which would still be slim at just over 200 pages) instead of forcing them into a pseudo-order with the aid of blurbs by the Pottermore team to try and make them "flow", though, and for that reason I don't think they're worth what's being charged for them, especially since the content was previously available for free. Perhaps I'd feel differently if proceeds were going to charity, as with the Comic Relief editions of Quidditch Through the Ages and Fantastic Beasts, but being ebooks and the dry and shallow vignettes that they are, it's really nothing short of a money grab. I'd only recommend them to the most hardcore of fans as they don't add much of value to the existing canon, and you won't be missing out if you skip them.