Debate goes on..........
Copper will freeze and burst, plastic will not
Plastic will be chewed by rodents, copper will not.
Plastic should be without joints where no access available, copper can be solder joints.
Plastic needs many clips, copper can be bent and looks miles tidier with stipulate clipping.
Looking at the pictures, I would have it redone (possibly partially).
Someone was talking about price issues. Surely less joints on plastic would be cheaper than what I see in the picture. Also, if CH, is it barrier pipe? Already said, plastic is better out of sight. If under tile and rodents have no access to it, I would use plastic (no joints). Ensure joints are properly support sleeved.