Those ramps on Metallica do look steep and i'm concerned about the left hand ramp shot. The opening is small and it's obstructed by the in line target wall - bet ya Metallica can't do back-hand flipper shots!
I don't know one of the band members is right into pins and has quite a few, he might
Kirk has a few pins, James has at least one (the custom whirlwind), they have a few also in their studio. I have seen a few vids that they have pins backstage as well. Great to see a band so into it, that is another reason I think this pin will rock, they wouldn't let anything not up to scratch pass through
Some autographed translites/back glass like Kiss come to mind.