My Dad got a 12ft pool last year and no heater so the pool was freezing but this year we got one and it has made it so nice I nerer andt to go in because I mght never come out. so yes they really do work just fit it to your pump. chris
They work well but they munch the electric like nobodys business....it'll cost a fortune to run.
I used a thermal cover on mine and it increased the temp by 8 deg C. They look like bubble wrap so it might be worth buying one of those.....it'll be a lot cheaper too.