While there are many tools for memorizing passages of text, I am not aware of any that let you pick the number of hint characters per word and also let you reveal hints as small as a single letter.
Study hints
Click the buttons to reveal the passage as you recite it, even if you think you know the line. This helps in two ways:
Catch mistakes that you did not realize you made.
Stay caught up so when you have difficulty with later sections, the hint is only one click away versus several clicks.
Writing questions
Keep lines short and place line breaks at the end of phrases. This makes advancing hints line-by-line easier.
Keep passages short enough so that you can see the entire passage and the buttons at the same time. Break longer passages into different sections and study one section at a time.