My Take
I really like this tool as it allows students to take charge of their learning. I like that there are multiple ways for students to practice the vocabulary words. It is not for everyone, but the students who like it really get into it. They keep trying to do better and get a higher score than the other students. For somethings, the app is a little too sensitive - for example, if you don't capitalize a word it that was entered into the program with a capital, it will mark it wrong.
How I Use It
I personally don't use it much, as I put all of the use into hands of the students. I create a quizlet class for each of the subjects that I teach and then invite the students to join the class. I then leave it up to them to create the vocabulary lists and the words they want to review. I do have to say that most of my students didn't choose to use this tool much, but those that did saw a real benefit. I think that greatest benefit came to the students who made up their own decks.