I have a tankless hot water heater at the back of my house. It took at least five minutes for me to get hot water to my kitchen sink for small jobs, and then I had to wait again if I needed hot water again. I couldn't wash a few things at a time in hot water while I was cooking. My new Waiwela 2.5 Mini Tank under my kitchen sink provides instant hot water until the tankless one provides hot water, and then the Waiwela turns off until needed again. I'm sorry it took me more than two years to discover this solution. It is wonderful! Also, the man I talked with at length at GadgetsGo was extremely knowledgeable, helpful, and patient with me as we talked through the problem I was having. He knew his products well and made excellent recommendations. Available space was an issue, and he even did extra research to find me the best unit that would fit in my space. I am a very happy customer!
Advantages: The Mini Tank fits under my sink (along with all the pipes and the food disposer) and provides hot water quickly until the tankless hot water heater kicks in to take over.
Disadvantages: I had to have another electrical outlet installed, but it was worth it!