I don't know how to tell if the NAGOYA is genuine or not or where to get one. I bought mine from Amazon and it was junk. It came in a green sleeve just like the ABBREE antenna and it said it was made in Taiwan. And it also had a BTECH logo on it. My antenna did in fact come from BTECH thru Amazon.
As for the AR5RM, it is a great little radio. There are a couple of very cool features in the menu options. One is the Scramble mode, menu 45. There are 3 tone scramble options there. Very cool if you want to have secure communications. And then to make it even more secure on top of that there is the frequency hop menu which scrambles the frequencies so if the powers that be want to listen it, it will make it even more difficult. That is menu number 41. Do 41 and 45 together and nobody will be able to decipher you. Well, I'm sure some alphabet agency might be able to but it would take some time. If you keep your transmissions short I'm sure you would be very secure.