I have a contractor remodeling a bathroom. My house is plumbed with 5/8" Vanguard Polybutylene (PB) pipe. He is using a Qest connector to connect the PB to copper to plumb the shower. His connector is plastic on both ends, a plastic ferrule, and a Qest metal ring with the ferrule. The shower is to be plumbed with 1/2" copper. I have looked through the Qest fittings but nothing jumps out as a better adapter (which I believe there must be.) I have a brass/plastic compression connector for 5/8" PB to 3/8" copper. If I can find a 5/8" PB to 1/2" copper would that be a better solution ? I have asked him to cut the PB above the ceiling of the garage, very close to the shower with the connectors accessible in the garage. If a connector fails, I have access and I also have opportunity to retrofit.