These Flowtron Bug Zappers work amazing. At first I thought the unit was broke because I heard so much zapping, but it was because the unit was just swarmed with insects. No complaints. I have the 15 watt, 40 watt and the 80 watt units. Note the 15 and 80 watt units both have a 3 prong grounded cord, but the 40 watt one comes with a 2 prong power cord. Not sure why that is, but it doesn't seem to affect the operation. I think the 40 watt size is the best bang for you buck.