I only use Tamiya primers now, out of a rattle can. As mentioned before, some of these red primers build up and hide some detailing. They make them in either metal & plastic versions or just for metal. Kinda on the expesive side but hey, it's a 700 dollar tank.
Can't answer the the question on what they used on the real thing. If the paint sticks well enough you'll never see the primer.
- Jeff