What is the difference between the Garage and Concrete Floor Primer and Recoat Primer please?

I am getting ready to paint my front porch with Rust-Oleum Garage Floor Paint. I picked up a gallon of Rust-Oleum Garage and Concrete Floor Primer. My concrete does not have a previous coating on it, but it is so severely stained that I thought a primer would be a wise choice. Please advise if it would be okay to use the primer after etching and before painting under these circumstances. I will also be using the cleaner and degreaser prior to etching, but I am not sure how much it will help the stain from the ash that fell for months during the Carr Fire. I also wonder what the difference between the Garage and Concrete Primer versus the Recoat Primer? Is one better than the other or is the Recoat Primer the replacement product? Thanks so very much for your help!