James K brings up valid points. Cold blue will not compare to a professional bluing job. It will wear faster than a professionally done finish and if done wrong you could potentially cause damage to your firearm. It also does not cost what a professional finishing will cost and it can satisfy that 'did it meself' hunger many people have. As for oil retention properties I can't say much...but I'm from the internet so I'm sure its fine
Below is a link showing a barrel done in Blue Wonder and a barrel done with Oxpho-Blue. Both were done in August 2010 after I inherited the guns. They had been left leaning in a single pane sliding glass door and had significant rust issues on the barrels. Neither is perfect, but I did not pay the value of the gun to have them refinished either.
The Remington 740 done with Blue Wonder does show wear at the muzzle from riding in a scabbard as well as a slight mottling and wear marks on one side.
The Savage, done in Oxpho-Blue, doesn't show any wear YET. I'm sure a few more coyote trips will surely ding or rub something.