As far as the tests go, they are done at home, so you can take as long as you want. (Well, of course, up to the due date ;-)) My daughter and I have differing opinions on why the exams seemed so hard in the beginning. She says there were things that she wasn't expecting on the test, and hadn't studied for. But the material was covered in the chapter. She felt like the teacher didn't emphasize certain things, but expected them to know it anyway. I wasn't involved enough to make a judgement on what was covered in class vs. what was covered on the test. However, DD did improve over the year, and her test grades went up significantly. My suspicion is that she didn't study very well for the early tests, but quickly realized that she needed to know the material better.
The teacher did do a brief review before the exams, but not significantly. It seems like the tests were mostly answering questions to the best of their knowledge or fill in a large blank type. DD tends to want to be extremely brief and assume the teacher knows what she is talking about. She is getting better, but it is always best to give as much info as you can come up with , KWIM?
We did not pay for any extras from the web site, but the study info was helpful. I think, as with most teachers, there is an adjustment period, where you figure out how they want questions answered, and what they expect. This teacher was very good about responding to questions, and offering extra help if needed. And there are a lot of assignments, so the grade is not so dependent on just the exams. I bet your DD will do fine. It all comes down to study time and effort.