There are rust ecapsulators and then there are acids like phosphoric solutions that do kill rust and but not coat it, but leave a phorphate sort of dust like material there which I wipe off unless I neutralize it with water. Again I will mention if that acid is not neutralized there an be a reaction to primers, especially they also contain an acid. Some epoxies and etch primers. I do not like to the water on it, seems to void some of the acids work. Some might say the acid must be neutralized or it will eat at the metal long term?? .I have been told by body men Pros ( of which I readily admit I am NOT) NOT to use the rust ecapusators, under any area but maybe the inside floor pans. Not on exterior that must be and remain perfect. I mention this not to argue with anyone or put down Eastwoods products. They have excellent products but I have found that for body/paint, to go to the pro shops, like local PPG store, Southern Urethans, TCP , et....
Several decades ago, I have used PPG acid prep products worked great but very expensive so I have found some alternative products.
I am always looking to learn and improve my methods.
I am like many, I can not afford to pay a shop $5-6000 for paint work, especially on a car that will never justify that investment, so I plug away doing it all myself. Fortunately I build what most of us all drivers! not perfect show poodles.