Commercial photographers didn't use polaroid cameras to test lighting. They used Polaroid film in specially made polaroid film holders that attached to medium format cameras in place of the normal 120 film back, or that fit in a 4x5 camera's film holder slot. The results needed some interpretation because Polaroid film gave a different look than the E-6 films most of them used for the final image. I think an old digital SLR would be best for this today, given the extreme cost of instant films now; I wouldn't see it as a 'sin' by APUGs ethic because you're still going to use film for the final image.