Heating domestic water by harnessing the power of sunlight is nothing new, and even in the UK people have been heating their water this way for many decades. As energy gets more expensive (and you ain’t seen nothing yet!) getting “free” hot water is more appealing.
Evacuated tubes are generally more efficient offering better performance in spring and autumn, and when the sun is at an angle to the panel, but may have a more limited lifespan, and are not always considered aesthetically pleasing.
Flat panels are simpler in concept, basically black pipes in a glass fronted box, but can offer vast amounts of hot water on sunny days.
Overall system efficiency will depend on the control and pumping system, and the hot water tank design, but overall the systems are simple and reliable.