The key to a nice riding leaf spring is to reduce the inherent friction in between the leaves as much as possible. Those types of coatings would do the opposite
Blasting is obviously preferred method of cleaning them up for me but in the absence of that I have used a wire wheel on a grinder.
In the past I have sprayed them with a decent quality paint from a spray can. The key here is not to put the leaves together until the paint cures, this can be up to a week, or longer if its colder. Then after the paint cures I spray them with a paint that contains graphite. Let that dry and reassemble.
In the past I have used the stock antirub pads ( the plastic things in between the leaves) and just sanded em a bit till I got all of the metal out of em.
If I wanted the paint to last a long time I would just choose a higher quality paint and spray it through a gun. I would still use the graphite paint though