Interesting that they are marketing this for pools. I guess they can handle the throughput then, but it looks like copper piping which is not great for chlorinated water. Also the temperature rise is very little, less output than my heatpump - and heatpumps are sized at a fraction of normal heaters. The other thing, you need you head examined to try to heat your pool with electric resistance heating. Sure these things are cheap, but you heating bill will run in the thousands of dollars rather than in the hundreds. Electric resistance heating is the most expensive way to heat.

Look at it this way, I use an electric heatpump that has a COP of 5.9, what that means is that for each unit of electricity I put in I get 5.9 units of heat equivalent out. These things have a COP of 1.0, so it will cost you about 6 times more to heat your pool with one of these things than with a heatpump. Sure makes the choice very easy - buy a heatpump if you want to use electricity to heat.