The "jamb paint" as far as I know is nothing more than a color matched oil based alkyd enamel.
If you use it, make sure you use a proper enamel hardener. It will wear and hold sheen longer.
It also wont be effected if you touch up with monstaliner later on. Without hardener it will, as the solvents will lift it.
Though in my experience, jamb paint it isnt needed, especially with monstaliner that you can mix as much as you need.
Just mix a small batch, or dip into left overs as you finish applying the bulk of the project. Again, better if sprayed.
Spray goes considerably faster, and allows you to use more of that pot life if needed.
All of my jamb areas, sills, vents, door trims, and even touch ups for thin spots was done with actual Monstaliner coating and a foam brush.
Dab-dab dab makes for a decent texture, and will be considerably more robust than the jamb paint.
Examples...
vents....
Door trims came out with plenty of thin spots, especially around the screws.
You cannot even tell the touch ups....
The vent holes were done with foam brush and monstaliner as well.