Student Response System

I have recently been researching a tool for use in a classroom.  It is the "clicker", otherwise known as the student response system or audience response system (ARS).  I know some of you more seasoned instructors out there may have been using these little buggers for a while now, but I am new to the idea.  I really like the concept behind the system.  It is advertised to be easily integrated into PowerPoint and seems to be relatively inexpensive to implement.  The average cost of an individual clicker is about $40 to $50 depending on the system you use and the receiver can range from $250-$500 depending on the brand you purchase.  I have done estimation and determined that for a 30 person classroom (which is about average for us) it would cost roughly $1800 per classroom.  I do not know what the budget is for a K-12 school, but for a government institution, this is not a deal-breaker.  I think this is a reasonable expense for the payoff.  These little buggers can be used for formative evaluation, feedback from students and will let you know as a teacher if your message is being received.  I know in a larger classroom, it is difficult to get an answer or interaction with every student, this is one way to get that interaction.  I am including a couple of links to different clickers.  This is not an endorsement, but just the ones with which I am most familiar!! 
TurningPoint
Qomo