These types of heaters are often called “on demand heaters”, as they only heat water as it’s needed. This makes it much more efficient as there is less heat loss, and you will never run out of hot water.
Because there’s no tank, it does not take up a lot of room. Compared to traditional water tanks, these new models are very small and compact, yet produce heat at a higher rate.
One the disadvantages with this technology is that you will have to pay more, and depending on your water chemistry, they may not be a great fit. This is when it would be recommended to contact a technician and see if these models are recommended for your specific home.