Ok, finished both and got daytime pics. They don't look as good as I wanted them to. Up close they look kind of hacky and shabby. From far away they look fine, so that addresses half of my concerns -- one being unwanted attention from traffic cops, the other being a matter of looking professional when I arrive at work or at a job.
I struggled with the decision on how to mount the one on the truck. I had previously made some cleats that I would screw to the grille and then screw the sheet to them, I considered using silicone, and finally decided that 3 zip ties ought to do the job easily while being very easy to reverse. This turned out to be a good decision, because it won't last long. The material is too brittle. A piece broke off while I was cutting it, but luckily the sheet was large enough to re-mark and try again. When I was tightening a zip tie,
another piece broke off , but it was too late. I'm sure the end with the broken hole will crumble while driving.
Apart from the shoddy workmanship, the one on the truck actually looks nice (but will be visible from far away and grab attention). In the close-up of the broken bit, you can also see my shoddy edges and how they're not quite held flat against the grille. My plan was that they'd sit against the indented chrome edge that appears made specifically for the purpose.