Electric showers
An electric shower heats cold mains water on demand, so it works independently of your hot water supply and keeps working when the cylinder is empty. The trade-off is flow: the higher the kilowatt rating, the better the flow, but even a 10.5kW unit delivers less than a good mixer. Ideal for second bathrooms, loft en-suites and households where hot water runs out.
Thermostatic mixer showers
A mixer blends stored or combi-heated hot water with cold and holds temperature with a thermostatic cartridge. On a combi boiler or a mains-pressure system this is usually the best all-round choice: strong flow, stable temperature, no pump noise. On a low-pressure gravity system it can be disappointing without help.
Power showers and pumps
A power shower is a mixer with an integral pump, designed for gravity-fed tanks. A separate twin-impeller pump does the same job for a whole bathroom. Both add flow, and both add noise, moving parts and something else to service. Only specify a pump where the system genuinely needs one.
Matching the shower to the system
In short: combi or unvented mains pressure, fit a thermostatic mixer. Gravity tank with poor head, fit a pumped mixer or an electric shower. Anywhere the hot water needs to be independent of the rest of the house, fit electric. Always confirm the incoming flow rate at survey rather than assuming.