The idea and LED lights are pretty cool but one of the major flaws is that the coaster doesn't lay flat on whatever surface you put it on and that's because of the "pad" or whatever it's called in the center that houses the lights. It wobbles Because of this which while it hasn't spilled anything I've put on it YET it gives me a sense of uneasiness whenever I use them.These work great and are worth getting. I would call them a good valueI think the novelty aspect of these are pretty cool. They are efficient when you have a cup with a concave bottom. Otherwise, the cup will wobble since the button comes up slightly. There is an easy fix to this if you add feet to the coaster and keep the button facing down. For the price I would think that they should come with them.Light doesn't come up through the glass. Only out the sides of the coster. False advertisingHermosos! La batería es de larga duración