yea, as much as id like to believe that a flash is a flash, it has shown me over and over that 3rd party flashes (metz 58 AF2, 565, 568) are not as accurate as the nikon flashes and its known by veteran pros that on camera its nikon, and off camera, whatever youd like. I hope this shanny does better.
theres something else happening between the nikon (body/flash) thats causing them to be more accurate. just like nikon caused some 3rd party batteries not to work with their body in a firmware update. I think there some hardware/software that lets them communicate better.
People do have their notions, but I would not word it quite that way.

I put some metering comparisons in reviews of three third party speedlights in most modes (direct, bounce, TTL, TTL BL, and manual GN), as compared to the Nikon SB-800 results - seen at
Flash Photography Basics
There is possibly quite a bit more to it. I'm thinking TTL BL mode might show some other differences (which is only default mode that most flashes have today).
But of course, at least three standard facts always apply:
1. Reflective metering will always show variations, due to the subject in front of the camera. I think it is obvious that few of us give that proper consideration, if any at all. See
How Camera Light Meters Work for the obvious way reflective metering works. This is about the first thing we all need to know about metering.
2. It is the camera that meters TTL or TTL Bl preflash, and then tells the flash what power level to use. The flash could not care less if TTL or TTL BL, white background or black, direct or bounce, etc... And it meters nothing. The flash just complies, sets the power level difference requested, and it flashes. Probably possible that some particular flash might not get that instruction right, but for those flashes that just do what they are told, we do really have to look for other reasons (about why?). There can be several better common reasons. Brand incompatibility should not just be the first automatic assumption (for something that is done by the camera anyway).
3. Specific to direct flash in default TTL BL mode (commonly used by event photogs), D-lens distance can override and limit metered flash if it thinks the metered value is too strong for the distance that it imagines applies. The reason for this is that direct flash falls off with inverse square law, so the background is typically dark, which is seen when metering preflash, which typically causes direct flash to commonly overexpose the subject (i.e., #1 above).
But... most of our
zoom lenses very often in fact report seriously incorrect D-lens distance (they report total random nonsense, making up numbers), which causes TTL BL (the only default mode on most flashes) to be seriously wrong, very often, frequently causing serious underexposure. More of this obvious detail at
Nikon TTL BL flash - D-lens distance data accuracy
It is of course true that 3rd party and Nikon flashes should perform alike in cases 1 and 3, since it is the camera doing it. I'm just not too sure how carefully we enforce the exact same subject condition to our hasty conclusions though. Notions should take efforts to rule out the obvious. We need more evidence than just some guy talking.
My own complaint is that the stupid camera ought to offer two new menus seriously needed for flash today:
1. a camera menu to disable using D-lens distance, to prevent it from screwing up the direct flash metering. Zoom lenses are totally ignorant about distance. They report phony distance numbers that are very different at every zoom setting. Not sure even any one zoom setting is ever right.
2. a camera menu to directly select TTL or TTL BL mode (since is was removed from most flashes today), instead of the very awkward Spot metering. The flash system never spot meters, but it is only way to select TTL (on most flashes today) as a way to prevent D-lens distance from screwing things up. But few understand what Spot metering is. It can often help default TTL BL flash units indoors (for reasons other than Spot) but without knowing a few things, it is a probable disaster in bright ambient.
It would be so much easier to use and explain with such menus.
btw, whats your take on the pc port on the side? maybe for a radio slave connection? weird though. no contacts on it. nice they added 2.5mm pc sync as well.
I didn't spend much time there, but I don't think I understand the question? That page shows these ports:
External Battery Port
USB Port for Firmware Updates
PC Sync Port
I think you just mean the PC port, which has been a standard feature since the 1950s, for any use of a PC sync cord. Radio trigger or slave trigger are common possibilities, but speedlight triggers typically mount on the foot today (was not always true). Studio flashes have no speedlight foot.