simple test is to help everyone/anyone learn that 'iron' or 'ferrous' or 'magnetic' types of targets are not always going to behave properly.
The paperclip, in its original form or straightened out, usually 'behaves' like a good kid who knows how to mind his or her manners.
Sometimes, as you will learn, 'man' [size=small](either gender of the general reference to people)[/size] creates things using magnetic-based ferrous/iron material, but shapes them into an unwelcome shape for even sophisticated metal detector electronics and their operators to deal with.
Thus, while most nails, or wire and many other iron objects will behave, things like you making the paperclip into an 'O' configuration, or rusty tin, or bottle caps, leaves us with iron target challenges. Kind of like it displays the behavior of child during the 'terrible twos.'
So, all detectors will have some difficulty handling some problem iron trash. Your Gold Bug Pro, an Omega, an F5, an AT Pro, an MXT Pro, and even the FORS CoRe and Racer. That said, it is only one type of problem we can all encounter, and if the Discrimination is a little higher, than what you saw in the video, some of the high-tone blips from Iron might have been handled better, but it is going to bother us all.
But he worked that site with a mode and Disc. choice that I would have used, and I would expect such a variety of iron targets to be a little misbehaved at times. I also know that you can take your GB Pro and come see Keith or me and show us how it handles an iron nail challenge such as my NBPT, and I will guarantee you that it will be 'shopping season' at your house. I did like the F19 better than the GB Pro on this test, but it was still no match for the FORS or Racer.
Monte