PowerShowers
PowerShowers destroy the thermocline and most of the energy stored in a hot water cylinder is left behind in the hot water cylinder. They are only compatible with tanks using fossil fuel boilers and the cost of the shower is double that with a ShowerPowerBooster.
The cost per 5 minute power shower using gas can be 16p

Electric Showers
Electric showers use electricity and water at peak demand when electricity is typically 4 times the rate it is at off peak. It is also used when water supply is at its most stretched. Most electric showers last only 4 years and the shower volume that most produce is half that of a ShowerPowerBooster.
The cost per 5 minute shower delivering a volume the same as a ShowerPowerBooster at peak demand is 45p.