Mixer showers use water from both your hot and cold water systems, to create the perfect shower temperature. To increase performance you can add a pump if you have a gravity fed system. Sequential lever control. Thermostaticaly controlled.
"Bought this together with the matching single mixer tap. They look quality together in my ensuite. However not is all as it seems. had to return the first shower valve cos it was faulty..Took me a while to sus this out.. and that's not good when you've plumbed, tiled and finished a bathroom and you think it's your fault that the shower cuts out after 10 seconds. Nightmare! Screwfix great and exchanged it next day. New one working fine and it does looks great. (mine fitted externally.) Curiously getting slightly lower water pressure from this than the old Mira it replaced..Don't know why this is but gonna have to fit a pump now. Welcome to the world of bathrooms!"