Anyone here use Rust Kutter on their trucks?

This is what my Rear Diff looks like before and after two coats of Rust Kutter (phosphoric acid). Curious if people rinse the excess product off or not? I've seen some mention of both. I'm not sure if that will appear different after rinsing. I'll be replacing the springs shocks etc later so I'm just getting this main section coated for now.

 

Myself it might be the pictures I can not see a major difference.

Just what is this product supposed to do? How expensive is it?

 

Rust Kutter is the brand but it is a bottle of Phosphoric Acid, the primary component in most rust converters/encapsulators. It was like $20 for a quart spray bottle. Went through the whole laundry list of options for dealing with rust and it seemed that a combination of phosphoric acid followed up with linseed oil would be my best bet for preserving the rusty parts. I've been on the fence about whether or not I want to paint over rust/converted rust.

This video was helpful
https://www.youtube.com/watch?v=tu1n1POMg98&t=692s&ab_channel=RepairGeek

 

I will stick with blasting it is easier for me.

Then primer and paint

 

Coroseal and Rust-Oleum

 

^^^THIS X2^^^