I generally back-knot 2 pearls, pass the thread through the third and snip it off. The loose end has never come out whether I use Power Pro or (once upon a time, silk) and there is no place for for glue or nailpolish as it is inside the pearl. I think glue or nail polish is unnecessary with some threads, like power pro, and adds a bit of stiffness as does going back through too many pearls. Whereas one knot may be vulnerable to coming undone, two knots is plenty for security. That doubled thread really shows, so why make it unnecessarily longer than what is needed for security?
I am clumsy, but never had one I knotted come loose at the end knots. I bought a zapper, but found i didn't NEED it. I can't see how it adds to the strength and it is just another unnecessary gadget- like the tri-cord knotter, tweezers, or an awl, are. Good technique makes everything but a needle and thread, scissors and little clamps (to keep the pearls slipping off the thread before being knotted) unnecessary.
How many knots does Hisano back knot? I would take whatever she does as the professional standard. Take a look at your Pearl Paradise strand. How many back knots does it have? My Tahitian strand only has one backknot and a dab of nail polish. I use two lknots and slide the excess thread through a third with no glue, but obviously one back knot with glue is all you need- if using glue.