I will say this, I am the guy that shot and edited several of the videos of Dr Jacks' antennas. I personally have the scanner type on my Jeeps rack and it does receive very well both on the 700-800 MHz spectrum as well as the Air and Mil-Air segments where I use it. It has reduced some of the well talked about multi-cast issues we deal with on the MARCs system in Columbus, Ohio ans picks up Mil-Air better than any antennas I own, and I too have a few. I can't speak to the way he wrote and presented in the videos but, given the lack of stats and testing I too was actually dubious. I can say that the particular antenna I have and use is working quite well. I have had it mounted on my Jeeps rack for over a year now. The only issue I have ever had was the rubber washer on the NMO mount deforming.
I have a great deal of respect for PRCGuy. He knows his stuff. It takes a long time for new ideas to percolate through a crowd that is staunchly set in their ways. Amateur Radio folks are like that for the most part. My only advice is either buy one and try it for yourselves as some of us have done or continue to grumble while some of us move on. If you look close in my Avatar pic you may see the antenna mounted in the back center of the rack on the Jeep.
When I first read Jacks patent info and saw the design, what I immediately thought was not that it was a capacity hat, but an actual capacitor, which it would be if it had a second plate. Inductors create a magnetic field when alternating current/voltage is run through them, just like a loop antenna and we all know a loop antenna is a fraction of the size of the wavelength in question, like using a hula-hoop for 40 meters. Why can't this design work?
Anyway, buy one and try it like we have. You might like it. I do.
Sean
KB8JNE