Excel study guides across all subjects have a very nice layout and typeface, as Drongoski pointed out.
Some have described the content across subjects such as physics and chemistry to be lacking, but overall they are a solid textbook.
For maths, I feel as though they are kind of a waste. This is because there is an overabundance of questions available online, so buying them is debatable. Additionally, if you have a strong support group of maths friends, as well as teachers and WooTube that are able to help me understand concepts, then you may not need the short examples and descriptions in the Excel books.