How I Use It
I really like to use it for each homework question. Assigning one of the harder questions to do a check on how far students made it through the problem, and assigning one of the easier questions for a blanket check (almost everyone should have it, if not it definitely needs a reteach).
Sometimes I use it as a homework grade, and this provides an easy way to grade homework without collecting it or spending class time grading it. The only issue I run into is that I have to tell the students to put their name first in order to get credit (I can't find a way to require their name as a field?), but I have not done a diligent search yet to figure that out, it may be possible.
I also love using it with bigger classes to get feedback from some of the more shy students, and to push participation from everyone. It is a great way to start a discussion around a new topic as well.
Overall, I think its a great way to get instant student feedback, either about the homework from home, during a lesson, or as an exit ticket on the way out the door. It is completely free, and doesn't require you to purchase any clickers of any kind, and it allows you to ask open-ended questions (which the tradition clicker system doesn't typically allow). Great for more common core style questions.
The only downside is everyone has to have an electronic device with internet access in order to use it. In some classes for me this isn't an issue, but in others it definitely would be. In addition, some schools allow for the use of electronic devices for instruction purposes, where as others have a no tolerance policy. It depends on your schools policies and your own students whether or not this will work for you.