I swear by it, and nice info. as well Lupo.
I let the parts soak overnight, though my axle plates required maybe 2 days. A good bath 20 or so minutes in heavy baking soda to counter the acid. Baking soda leaves almost a phosphate appearing finish, at that point the parts clean up quickly. A lot of steps but it works. Too late for a tumbler
For heavier rust a concoction using Must for Rust, vinegar and water works real well. A board member came up with it.
The appearance of these plates is misleading because one is the "pretty" side - both plates came out equal.