I think that some antenna mfrs 'stretch the truth' a little to get people's attention. But there are few antennas that may be considered something new under the sun - so to speak.
As I have said on a few other threads about beam antennas, is that I talk to a guy locally that got one of these Joe Gunns recently. He had a Starduster before, and I could barely hear him from 13 or so miles away thru the urban sprawl of Silicon Valley. We discussed some possibilities for another antenna, and we also discussed the better points of the Joe Gunn against other antennas. A week or so later, he bought the 'Smokin Gunn II' and put it up with a cheap/effective Radio Shack antenna rotator. He also installed a home made choke balun.
We gave it a test between the distance. The claims of 2 S-units gain were NOT exaggerated by the mfr. It was audibly louder as well as stronger. Side-to-side db loss wasn't as high as the mfr said; seemed to work off axis nearly as well. The rear didn't have the db loss as the mfr also said it would. I think that it is a very effective antenna - despite some of the mfrs claims. I wouldn't say they lied about it; I would say that it was underrated - if anything. This friend can be heard loud and clear without any problem now; as compared to before. No doubt about it. It was quite a difference going between barely being heard - to booming. From starting off with in the low side of my receive meter - to the edge of the red 'stawberry patch' (starting from ~S-3/5 before to S-9+). He uses a Superstar radio - BTW.
Yes; I would call that change with just an antenna quite significant! The Starduster antenna sounded like junk - comparitively. Yes, the change I'd seen between the two was far more than 2 S-units. But I attribute that to the Starduster that had seen better days. Because the Starduster was in poor shape, the difference between the two antennas was more like 5 S-units - maybe a little more.
I think for the money spent, this beam is well engineered. It is light but strong; little wind resistance, can be horizontally or vertically polarized, and for the money provides tremendous bang-for-buck value. If I were to spend $350+ for a different antenna system (beam antenna and rotator, coax, etc...) or just getting into radio, that is what I would buy. From my listening perspective, I would say that it is one to look out for!
