Neighbour has one. For her is amasing as she stores it in a bucket.
You connect it up to the tap and switch it on with the other tap closed, the pressure expands the hose. Trouble is that when you open the tap the pressure reduces, so the hose starts to reduce in length. So you are always tugging on it as the length reduces to shorter than you want. So you always need to be using the hose on full pressure. You can't just let the water trickle out of the hose.
Advertising will sell loads as they don't tell you the 'cons'. But I can't see it becoming a revolution in garden watering because of the cons. They are also expensive.
Wouldn't work for window cleaning IMHO.