It is for aluminium, it has an acidic component to etch the material. That said I have left it in my aluminium pot spraygun for weeks, no real probelms with eating the pot out (looks a bit grainy though)
I believe the zinc oxide forms part of a sacrificial barrier in the presence of moisture.
Time will tell if it will do the job, certainly better than bare metal on bare metal with dust/crud in between.
Spare bare 6061 channel I have in the shed is suffering from filiform corrosion just from dust accumulation, whereas the dusty primed scrap parts have none.
My main reason for using it was that alodine and other hexavalent compounds are too hazardous to the body and environment, especially trying to dispose of it safely.