Steve -
I've used Alclad and other metal finishes over Stynylrez, worked very well for me. Being a soft paint as primers are, which lend themselves well for sanding, I found care was needed to ensure no marks are left behind prior to the metal finish. For my own use, I found the Stynylrez metal primer did not work as well as the plain old gray, I thought it was a bit less user friendly. I had better results with the plain gray, during the final prep work before the Alclad.
When I sand for final prep of the primer, I use the finer grit polishing pads as they are less prone to leave sanding marks, as opposed to the more defined edges of sandpaper. It takes very little polishing to ensure a suitable prep for Alclad, just enough to be sure it's all leveled and any grit removed.
If you're going for a really bright and shiny finish, then a smooth black coat works best. I finish only as clean but not highly polished, like an aircraft in service, so the gray primer works very well. My relationship with the black and white Stynylrez has yet to become cozy and comfortable, seems quite a different substance, especially the white which seems rather "chalky." The gray is my go to overall primer.
It's said it dries quickly, that seems so, but it works much better for me if I let it sit at least overnight, rather than to sand quickly.
Patrick