Those plumbers may be noisy, but it's great that they're doing quality work. It's cool your husband gave them props for it.
That bank loan rate at 2.87% is seriously a steal! Way better than expected, right? Too bad about the mix-up with the copper and PEX pipes though. Costs always seem to creep up in unexpected ways. When it comes to tipping, if they're doing a solid job, showing some appreciation never hurts.
If you're still hunting for reliable plumbing help, I recently had to call in these London plumbers from pm247.co.uk during an emergency, and they did a pretty solid job.