This is the 4th unit of this type that we have purchased. We love the instant hot water so much that we consider it a necessary part of our kitchen. I bought this to replace a 6 yr old unit that developed a leak around a seal so the installation was pretty much plug and play taking less than half an hour. Plugged it in after filling and flushing and we had our hot water again. 
This unit unlike the others, rumbles like boiling water whenever it goes into heat mode. We never noticed this in the other similar units. I turned the temp down and it is still noisy just not as often and the water is just warm. This is so loud that we can hear it in another room with the TV on! I dont know if ours is defective or if Insincerator cut back on the insulation! Not sure if I would recommend it or not.