We like the book set. My 5 year old loves the pictures and the characters. The language is easier than stage 3 from "I can read" which is what we bought first. If you compare the difficulty level to the Oxford Reading tree, level 1 from "I can read" might possibly be level 3 from Oxford reading tree.
There are 12 little books in the collection. They are not bound but stapled in the middle. Each one has a different subject, e.g. "short a", "short e" etc. On the first page there is a little review which words you will find in the story, e.g. "sight words" like "all", "and", and the words for the chosen subject "short e vowel sound. They are listed and you are asked to sound them out before the story starts. I found that not very practical because my son really wanted to get on with the story!
He finds the books really cool which is better than what can be said about the Oxford reading tree books (although they are generally fairly funny). The short length of them is actually an advantage as he is not quite as put off as with longer books. That doesn't mean he runs to them every day and wants to read them which I was secretly hoping for. It's really a struggle to get him to read in general though these books hopefully will get us a step further!