have i had cheapo ones fitted as I am getting backflow contamination, especially the kitchen one.
I can't tell what you have had fitted!
Nor can I tell what you H & C supply arrangements are
At the moment you are assuming that you have backflow problems caused by taps - there are other possibilities (shower mixers/controls have been mentioned twice in this thread) but you need a methodical approach to identify the causes rather than assuming a cause.