This has been an interesting thread. I found myself looking at the flats on stage at last night’s panto rehearsal and nodding sagely. “Ah… someone’s been and turned a pozi screw with a Philips driver, and now look at it…” 
When I built sets for a theatre company, we always used Roberston screws. They worked much better with power drivers than other types of screws, and made for very quick and problemless take-down when we did change-overs.