I've read all three of the MBS books. They are all interesting and good. It's worth it to go to a book store to read the first part of the first book, which is funny and clever.
The book follows (what else but) an orphan as he responds to a newspaper ad for a child seeking "extraordinary opportunities". When he responds, he joins a number of kids for a written exam. The exam is absolutely impossible, and some kids leave the room in tears.
Nevertheless, the boy uses his exceptional brain to pass the test. Other tests follow, and in the end, he and three other kids have all passed.
What follows is a tale of adventure and danger, intellect and puzzles. The four kids have to team up to save the world from a mind-control device. Needless to say, they succeed and go on to other adventures in books 2 and 3.
These books reminded me most of "7 Professors of the Far North". But it's been a long time since I read that one.
These books aren't deep reads, nor do they have themes beyond using your gifts and working as a team. But they are fun.