I've used clickers since I started teaching. In some classes/lessons, I use them extensively. For example, my novelty and statutory bars sections of patent law are almost all clicker exercises, where I vary the hypotheticals just slightly to test the outer limits of what constitutes, say, "public" use. I think of it as lightning-round Socratic method, except that everyone participates. I also like to use them because it forces the students to take a position. I routinely get many more votes than I do hands raised when I just ask.
I also find that clickers embolden some to speak up, because when I show the totals and that many people agreed, students are more likely to raise their hands and explain their answers. This is helpful, because it allows me to figure out whether the class is understanding the material and, if not, to find out why. The clickers can also scare students off - if only one picked an answer, he or she is less likely to volunteer why. It frequently happens, though, that the minority of one was correct or recognized some nuance in the question. Thus, I use a belt and suspenders approach - get clicks, ask for hands, and then show the results and ask for more volunteers if need be.
I recommend clickers to anyone not using them. I find them helpful and my students have responded positively for years.
But as the ABA moves toward requiring formative assessments (Standard 314), I wonder whether the clicker slides are enough. On the one hand, the students answer questions and we discuss right, wrong, and iffy answers and they can judge for themselves if their responses were correct. But maybe that's just me being lazy and not wanting to do more work to change my methods. Perhaps it would be better if I required everyone to answer (my participation rate runs at about 2/3) and graded answers (I have colleagues that do this).
I don't know the answer to this question. On the one hand, the students are responsible for their own education and should participate as they wish to their benefit or detriment. On the other hand, maybe it would be better to have more grades spread out throughout the year. I'm not sure my students would like that so much, but the educational results may end up improved.