I also recently acquired a 4-in-1 brush for prepping copper pipe and fittings. I've had separate brushes for the insides, and sandcloth for the outsides before, because I'd acquired the different sizes over time instead of needing to do 1/2" and 3/4" all at once. I needed a new 3/4" inside brush because the existing one was getting smushed and rusty. I've still got a supply of sandcloth for dealing with tight spaces, but the 4-in-1 brush does an awesome job cleaning off the oxidation from the insides and outsides of 1/2" and 3/4" pipes, all in one tool instead of 3.
All that to say I was able to do a couple loads of laundry this evening, and I have the outside faucet working again, too. That just leaves running new pipes to the toilet and sink in the old bathroom. Woohoo!