The answer is: not much.
Unfortunately I wanted to give this a higher rating, because honestly: The characters have nice interactions, are well written, are as charming as they are in their respective anime with their unique quirks - so to speak.
It definitely is entertaining and if you like the characters, you will get a bit more of them and see how they act off of each other. However, it's really just "a abit", which ends up pulling my enjoyment down. Like, I would love to see more of it - but as there isn't, it just leaves me with a unfullfilling feeling.
Just look at the picture for it: You already have 4 maincharacters, 4 main supports, add 2-4 other supporting characters each, add a few more for teachers and then give it the average length of half a normal anime. You don't need math to figure out, that this adds up to barly any screentime for most of them. As a result most of them have less spoken sentences than there are episodes.
With that in mind, there is simply barely enough room for characters to interact with eachother, let alone build any kind of relationship or having some kind of arc or developement. Frankly such a side-show doesn't need a character arc - but when for example one characters announces a rivalry with another character early on, I'd like to know this acutally means anything. But given the setup, there is a chance they won't even have any direct interaction before the anime ends. It's more like "Remember that? - The Anime". Remember how Ainz knows powerfull magic? Remember how Tanya is sadistic? Remember how X is lazy, Y in love, Z is loyal? Interaction usually touch the "How would those to react to eachother", but as stated before, doesn't have time to go anywhere with this.
The few times characters are actually interacting, it feels like a great setup for further developement. You see two characters talking about a topic and think "Wow, I didn't expect them to get along so well, I wonder where this will be going", but it doesn't, because you got over a dozen other characters fighting for screentime.
This could be a proof of concept. Having a crossover of several good and beloved anime can be really entertaining. I even have to admit I liked some of the characters more in this one, than I did in their own anime. Which makes it even more disheartening, to know the show is ending before anything happened.
