I love that I can create a short, medium, or long length formative review for my students. I use the multiple choice format, and my students work in groups to answer the questions. We can all work at the same pace, or the students can work at their individual paces.
My students like to use socrative, because it allows them to be competitive and then we can discuss their answers as a class once the assessment is complete. Unlike a pencil/paper quiz, they get immediate feedback, and I can help to clear misconceptions.