Almost every home in the western world has hot water. The way they achieve that varies enormously, but it is pretty plain that this is a huge market. So what exactly makes up a top selling electric tankless hot water heater?
The general advantages of the tankless hot water heater are fairly clear - they provide water on demand without taking up a huge amount of space. If we compare them with a hot water tank, this space issue might seem the important one (unless we have a too-small tank that is always running out of water!)
In truth electric instant hot water heaters might not offer a huge electricity saving over modern electric tanks that are very well insulated. This is why a top selling unit makes a big deal out of the size of their unit. And to be fair, they are impressively small.
An electrical tankless waterheater sells well if it finds a clear target market. Their miniscule size for example can make them ideal for stowing under sinks for additional hot water.
The fact they simply plug into the electricity supply means they are unequalled for convenience. This is one area where they beat the natural gas tankless water heater hands down.
As it happens, the biggest electric water heater company in the world is Ariston (otherwise called Merloni Termosanitari) - it makes and sells upwards of two million water heaters each year and sells them in 154 different countries. As I said, it is a big, big market.