ZR is an excellent primer. I tried to use it as a top coat with their crystal coat and the crystal coat didn't work so great. Maybe if you used a better clear it would have.
If your substrate is ok, no loose or flaking, ZR would be fine. I used it on my truck in a scuff and shoot and it worked well. The ZR faded but I shot PPG DAU on top of it and no rust through.
