Which pipes are best in screed - copper or plastic?

[DIY SOS]

After a mains leak we have had the pipe work repaired by the builder. It is now ready for filling again with screed before the new wooden flooring can be laid. See attached picture.
My question is why the need for the copper length between the blue mains pipe and the white pipe leading to the kitchen services? Would it be better for the White pipe to connect directly to the blue mains? Thereby not having the copper pipe at all. Or is there a reason not to have this done in the concrete? The builder said he prefers copper as it is stronger, but I would think it better to have a longer plastic section in this scenario as this will mean there are less connections in the concrete.
Any advice appreciated.

 

[Newboy]

Dreadful bit of work - 4 buried couplings, unprotected copper, bend radius too tight and (judging by the photo) possibly too shallow.

What are the other two pipe runs?

 

[Roger928]

Yes terrible. No excuse for the likes of that with conduit pipe systems available..

 

[steve32]

Copper with soldered joints tested and insulated before floor made good.
Obviously your builder has no idea

 

[DIY SOS]

The other two pipe runs are both feeding the underfloor heating I think.
Initially there was only one buried coupling. The one that failed. But the plumber who was tracing the leak went through the underfloor heating and also the mains pipe, hence there are now four couplings!
I don't think there is anything we can do about the two new ones in the underfloor heating pipe, but I would like to reduce the couplings from two to one in the mains pipe.
What is the best way of doing it. With plastic pipe or copper pipe connecting to the blue mains pipe?
We are having to replace 50 square metres of flooring, so don't want to have to go through this again!