Some feedbac: I think the book starts off well but that as it gets later in the book I felt like it mentions concepts once and doesn’t really go into detail on them before testing on them.
There is only one test on each concept too. If you didn’t grasp it before and got the wrong answer then there are no other questions to test whether your understanding is actually correct. That then leaves you proceeding to the next section unsure that your uderstanding of the previous section was correct.
The feature I’d request would be maybe a few more optional exercises to help hone understanding if they got things wrong th first time.