Is it common practice to use plastic pipes and push on joints in a new Extenstion

[HarleyKelvin]

I'm having a new extention built which will include an ensuite and a new combination boiler. I have noted that the builder has used plastic pipes connecting to some copper pipes using push on connectors, also some plastic pipes are reccessed into the brickwork and will be used for a radiator. Is this now common practice? In my day it was all copper pipe. Will these pushon's withstand water pressure?