This topic has as many opinions as there are people. Personally I would talk to the manufacturer of the primer I am going to apply over the bare metal and follow their directions.
What one manufacturer recommends may not be what a different manufacturer recommends.
At the cost of materials as well as my time I will not play home chemist and find out later on I didnt know what I was doing.
Call me lazy, but it is much easier to call BarryK and get the straight info before shooting his epoxy onto my project.