I think I'm approaching this from a different perspective that many people here.
As said, I never claimed to be in expert in the minutiae of the phaser props from TOS. That's not how I'm looking at this primarily.
What I am though is someone who has had a long-standing fascination with confidence men and cons and forgers and forgeries. I've read a lot on the subject over the years and see certain patterns emerge that I think I identify here.
I'm also active in the firearms collecting community and fakes are common there. (Typically common firearms embellished to appear to be rare firearms or owned by famous people, etc).
People have been making forgeries and fakes of works of art for hundreds of years. There are numerous examples of forgers who have fooled experts, and museums and auction houses in the 20th Century. There are people who could copy an artists style, use appropriate materials (although not always 100% correct), and use techniques to properly "age" or damage an item to make it look more authentic. Why? the motive is almost always money.
When you combine the forger's art with the con man's skill at deception you can fool experts, museums and auction houses. A simple search will turn up plenty of examples.
The same is true now with props. In a way these are modern art works. There is a huge financial incentive to create a highly desirable prop. We've seen experts, museums and auction houses deceived in the past.
In addition to making the actual item the forger has to take on the role of con man and create a story that goes with the fake. It has to be convincing, work within known facts, and, hopefully, (for them) explain away any inconsistencies or "missing links" in the provenance.
History has shown us that this is often easier than you might believe. The problem is "the mark wants to believe." The auction house wants to believe something is a previously unknown piece for the money it will bring in. The potential buyers want to believe they have the ability to buy something that is typically unavailable on the market for any price. That desire to believe can, and does, blind people to problems with the item itself and/or with the story behind the item. And even the experts might "want to believe" because finding a previously unknown surviving prop is exciting and is a neat connection to the history of the show.
The existence of a previously unknown surviving "Hero" Phaser is an extraordinary claim that requires extraordinary proof. The amount of money that will be asked for it at auction alone demands that.
The first step is the provenance. The story and the documentation to back up that story. I see the story that this was in Wah Chang's hands when the show ended and was transferred to someone else sometime after that. The next thing I'd want to see is the documentation behind that story. Who was it given to? What was their relation to Wah Chang? Do they have any documentation of their ownership of this item in all the time since then? Can anyone collaborate this with even a, "Yeah, he showed me that in 1990" or some such? Or does the owner have any old photos showing them with the item that were obviously taken years or decades ago?
I don't see the Letter of Authenticity posted on the auction site. I'd really want to see what it says and how it explains the chain of custody over time.
Personally, the story as told, seems suspicious to me without more documentation. I find it incredibly convenient that it says, "This was given to Wah Chang to be reworked or repaired" precisely because that is the type of thing that can be used to explain away any questionable elements of the item itself. "Oh, that's different because Wah Chang changed it." That's typical of the type of story used to back a con.
Then there's the item itself. This is where the experts come in. And this is where I say I'm not in expert in the details of this prop. Although you'd think you could leave authentication to the experts, you have to remember that whoever creates a forgery is specifically TRYING TO FOOL THE EXPERTS.
Let me repeat that. A forger is deliberately TRYING TO FOOL THE EXPERTS. He'll use all available info to create as close a match as possible including material, dimensions, paint color, etc. The less information there is publicly available on any item the harder it is for him to have the knowledge to duplicate it well enough. The more info available, the easier it would be.
Is there enough info about the Hero Phaser to create a convincing forgery? I tend to believe there is based on the photos and measurements and discussions of the details and techniques I've seen discussed in the past.
Now, I don't know Jein personally. I've interacted with him online briefly a few times. He's always struck me as polite and knowledgeable. I would consider him an expert on Star Trek Phaser props (unlike myself).
However, that doesn't mean he can't be fooled. It doesn't take anything away from him if he is fooled. As said, the goal of the forger is to deliberately FOOL THE EXPERTS so they can cash in on the completed con.
In the history of forgeries in the art world, in the gun collecting community and in the prop community, there are plenty of examples of experts, museums and auction houses being fooled. So, a mere "This has been authenticated by an expert" doesn't really hold as much weight as you think it would.
(As an aside, someone has mentioned, "Jein has been fooled before." I don't know if that is true or not, or the details if it is, but if it is true it speaks to the point "That even the experts get fooled." )
In the art community the techniques for ferreting out fakes have improved with technology. They are past, "It looks right" and into analyzing the chemical composition of paints used (modern paint used on a 500 year old painting is a tell) and similar techniques.
It seems to me we're still in the "It looks right" level of authentication in the prop community. Combine that with the fact that "The mark wants it to be real" and you'll understand my skepticism.
Personally, I also, "Want it be real," because I think it would be cool to have another previously "lost" prop turn up from my favorite show. And if it is real, and this different from the other known Hero, that adds information to our understanding of the original props.
But, approaching it from the point of view of someone who enjoys reading about forgeries and scams and con jobs, I'm seeing a lot of the same red flags that have been raised historically in other cases of forgeries (usually art forgeries) and ignored until the item was later proven to be a fake. The provenance being the big red flag, the convenient story of "Why things are different" being another, and then the discrepancies (as pointed out by others) in the item itself being the third red flag.
Believe what you want. But extraordinary claims require extraordinary evidence, and I don't see that here, yet.
Thanks for keeping me honest, guess I'm not infallible either 
