Very interesting thread. I will add my experience, NOT theory or conjecture, but my own experience from doing home inspections for almost 21 years.
I have been in homes by myself more times than I can count.
I have had Realtors come by hours before I got there and unlocked the door.
I have used a key that was left out by the homeowner, builder, or Realtor.
I have been given the combo to the lockbox a gazillion times.
The Supra key didn't work out for me, so I have to say I have little success using it.

I usually do not lock the doors behind me when I go into the attic, or crawlspace.
I don't care how many people are there at the inspection - because I was hired to inspect, not babysit or be a social director.

With 20 years and 9 months and several thousand inspections under my belt, I have only had ONE case of someone accusing me of damaging or stealing something. Not even a phone call!

BY the way, the one complaint was a woman that said I ruined all of her clothes with drywall dust when an attic hatch fell down a week after I was in her house. I settled with the BBB for $12.00 to cover cleaning costs. She wanted $600, but I showed the BBB photos of the damaged hatch, and her photos only showed a little drywall dust on a couple jackets.