Personally I had my best exam results when I did exactly that, I wrote as much as I could for each historical exam question. I would research from book, lecture notes etc.
However, I wouldn't pay for this service when my lecturers and teaching assistants would do this for free and as they were the ones setting the exams I would prefer their advice than that of an unknown person.
However, I wouldn't pay for this service when my lecturers and teaching assistants would do this for free and as they were the ones setting the exams I would prefer their advice than that of an unknown person.