I've done 10 of them - by the last few I was able to get the entire audit done in less than 10 minutes. I usually had the interior questions answered before the manager made their way to the counter
Dress code wasn't a problem as I did them on my way home from work, but I also found that 0/10 stores know or were able to locate the actual model of their cash registers (brand wasn't a problem to ID). I found the managers universally friendly and nice to work with.
I'd definitely pick up as many of these as I could if they do it again - well worth the pay.