One inherent disadvantage of plastic tube is that it can be eaten by rats and squirrels!
Sorry but i must disagree, what is wrong with plastic, its quiet, it requires much less hassle to fit under floors, its as cheap if not cheaper than copper, it aint gonna get nicked by ***** gits, and i use it ALWAYS where it is not visible to the customer .
How many squirrels do you have running round your house !! or rats for that matter.
The only damage ive seen from rats so far has been on electrical cables, both in lofts and cellars and i go in a lot of rat infested cellars in Leeds areas i work in.
I think its a rather old fashioned attitude to have to plastic pipe, sorry for the rant but i can use copper as well as anyone i know and take great pride in my pipework but plastic can be a godsend.
No offence Agile.