For those of you in the process, or thinking about using metal roofing with exposed fasteners: We've done more replacements on this type of roofing than I would have expected. The main problem is 95% of the time from the screws rusting out.
Brand doesn't seem to matter.
This is what I replace the rusted out, usually #9 screws with: http://www.roofthings.com/12-stainless-steel-screw.html or google can find other suppliers.
That company also sells screws with painted stainless steel caps on regular screws. Those might be okay, and certainly if you need to match a dark color, I'd go with those rather than the screws sold by the places that sell the metal.
It looks like to me all the manufacturers get the metal from the same supplier, and probably the screws too. I expect their roll forming mills probably come from the same place too, since one manufacturer's stuff fits everyone else's.
I'd recommend spending the extra money on getting standing seam, which doesn't have exposed fasteners, if you haven't gotten that far yet.