My class uses these during group presentations, serious question & answer formats that require feedback, and just when I want to take a quick survey. I've laminated them and I keep them on binder rings and they turn them in when they switch classes. However, these could stay in bins too.
I am implementing the whole "students give feedback on other student's answers" idea in my classroom to help them understand other opinions can be correct too. This helps solve the issue of what each of us thinks. After a student states their opinion, each student is given a set of three of these (see the disagree and not sure cards), each in a different color, and they hold their opinion up. This helps with shouting out and I can take a quick assessment of their answers. Also, I am able to pick students who can give their valid opinion.