To be fair, those are Remtronix's claims not mine. I'm just wondering if it might work better for VHF/UHF airbands than the Diamond RH77CA..
I did not mean to suggest that you were making any claims. I did see the claim in advertising for the antenna.
I suspect that the antenna will perform about the same as the Diamond. It is tuned for 144 and 440. Too short for VHF air and too long for UHF air. It is a ham radio antenna after all. It is not intended to be broadband. The air bands are so wide that nothing but a discone will cover them. Alternately a quarter wave whip set for the desired air band frequency will out perform the Diamond or Remtronix.
It is important to keep in mind that Japanese antennas are tuned for their ham bands. Two meters is 144-146MHz and 70cm is 430-440MHz over there. I asked in a ham radio store in Tokyo (Rocket Radio) if they made antennas for the US bands. The answer was no. They do, of course, make HT's and mobiles for US bands to sell in the US.
That said, for reception SWR is not very critical compared to transmitting. Also, with one exception (the Diamond SRH320A) I have never had any HT antenna show a low SWR when attached directly to my antenna analyzer. Too many variables, I guess. Even with the 320A the SWR rises quickly outside the ham bands. By the way, that antenna might be worth trying for Mil air since it is designed for 144/222/440.
I should mention that the old RS 800MHz and the Remtroniix (same antenna I think) are dramatically better on 800MHz. Many years ago I had to be in the area of LAX for a meeting. I programmed the LAFD 800MHz frequencies into my scanner and tested several antennas. The RS was so much better I almost couldn't believe it. As I listened there was an alarm for my hotel! False, but I heard the whole thing.