Many thanks JFDIY and Moonshine - really helpful and I understand it so much better now.
Looks like radial is the cheaper, easier option, so I am still slightly confused why one of the companies who’ve quoted for us have proposed a branch system for those reasons ie they say it’s easier to install and lower cost (at least for our new-build - a simple rectangular SIP dormer bungalow with 3 bathrooms across the two floors).
Cheers.
PC