Review (5/5): I love them.
You will go through a lot of soap but this brand is the one to buy.
I discovered the first one about 40 years ago when a hotel guest put it into the washing machine. DON'T DO THAT! It ended up wound around the base of the inner tub and one end stopped the pump.
This one rinses out clean in seconds so it never needs to leave the shower until it is worn out. I usually get about 2000 showers or 5 years out of one. Where I live these are for sale in most stores that stock bath tools, but the convenience of Amazon makes that trip unnecessary.