If the panel is thoroughly sandblasted to remove all traces of rust, then sprayed, filed, and finished both sides it's guaranteed not to rust out for 5 years. I can do the same with plastic filler on a similar panel, so I'm not impressed.

A panel like their website demo panels, that was perfectly sound except for little holes reminiscent of #7 birdshot, might be suitable, but leading would be even better and far more permanent.

I'd take time-tested hot lead over cold tin/zinc spray any day.