Honestly, was going to give the book 3-stars because of the annoying $%^& Miledi. She's that annoying. Apparently, however, she's supposed to be. So kudos to you Shirakome sensei for making her so utterly annoying you have truly achieved your goal.
It is a lot of fun to see some of the origins of the main line story. If you haven't read the main series, I'd start there, not because you won't understand this, but it might give you a different perspective on things than reading the side story first.
Verdict: It's Arifureta. If you like the world, it's worth looking up.