But arguably vanishingly minimal, as demonstrated by the tiny amount of friction loss shown in the tests. Certainly insignificant, given how slowly chains wear.

FWIW, I haven't used any chain-cleaning device in decades. When I hear a chain start to squeak, I drip some chain oil onto a plastic produce bag, grab the chain with the bag, and backpedal until it looks as if the chain is lightly coated. I wipe off the excess and ride.

That's it until the chain squeaks again, many hundreds of miles later (unless I ride in the rain at some point, which moves up the schedule.)

I'm always amazed by how long my chains last.