Yes, it works to remove rust and even old paint. Kind of cool, really.
It does take a while. Sometimes a couple of days.
The part doesn't come out shiny-clean, but definitely free of rust.
Usually we'll "zap" the part for a few hours, wire brush it by hand under hot running water to remove loose crud and paint, and repeat until it's clean.
It is a line of sight process, from the surface to the sacrificial anode. having several anodes helps a lot.
one trick I picked up on the internet that really works is finish-cleaning with grey scotch-brite. it works, and for some reason the grey seems to work better than the other scotch-brite pads. It removes the black inert iron oxide residue that's left.
experimenting is as easy as putting some washing soda in a bucket of hot water and submerging the part in it with the battery charger connected as prescribed. simple. cheap.
I still prefer the sandblaster because it's so much faster, and the part looks prettier - but this is a good alternative for non-sandblast-able parts.