Medium To High Grade Rust Inhibitor And Hydrochloric Acid? What's The Difference

The principle is completely different. Hydrochloric acid is yellow in color and forms rust water by dissolving iron and attaching it to the steel surface. Zhonggao brand rust agent is a rust inducer that induces its natural rusting ability and makes it develop into a stable rust layer in a short period of time (about 30 days).

After the rust layer is stabilized, will it not fall off even if it is rubbed hard?

No. The weathering steel rust layer will be very strong after stabilization, but it is not absolutely permanent (if it were absolutely permanent, the service life of this steel would be permanent). A small amount of rust will fall off if wiped vigorously over a large area.