He's an idiot from a technical point of view, because it probably would have worked just fine. However, he only gets paid for successful installs and for any upsells, where money from all such upsells go directly into his pocket. What would you have said if you were he?

I'd get a different installer and not mention the first one. Chances are good he'll just do it and it will work fine.

It will probably be just fine. Always install solid copper, but if CCS is already there, use it until it's proven to not work.

Thanks I appreciate your feedback. I'll give it another shot.