It does fit on the D850 and you do get the 9fsp as advertised. The build quality is not that good as I have attached it to my blackRapid sling with my 24-70 lens connected. My concern is that this device now carry's the weight of both camera and lens and I feel it it being pulled apart at the joint as I walk and i put my finger over the joint. Also it is not sealed against rain as I used my camera in the rain and I saw some splashes in the battery compartment (but i doubt that would do harm to the camera.
since it is made from plastic it also very easy to scratch.
however if your objective is to use it with supplied neck strap then consider my rating as 5 stars..

The good: It fits well onto the body. Even though it is plastic the grip itself felt solidly built. I liked the joystick better than the one on the body of the camera itself.

The bad: The power on/off button did not work consistently, and it was VERY hard to move. The command dials were not very "clicky". It wasn't as easy to set stops because of that. (I did expect that one, though as it is much cheaper than the Nikon Grip). The biggest issue I had with it is ergonomics. The thumb curve on the back of the grip is fine until you have to reach the AF button or even the wheel. I have normal, if not slightly large hands, and I still had to move my hand off of the grip to the side to reach that AF button. I use it exclusively for focus. I don't use the shutter at all for that. It helps with recomposing an image after framing without having the focus accidentally tripped by the shutter. Not being able to reach that button and having to take half of my hand off the grip. That makes the grip useless as a grip because of that. That position causes my hand to cramp up after a while. If I can't grip it completely, what is the point?

This grip is great on the D850 - no flex at all between the grip and body. Color matches the body perfectly. Overall quality and rubber are excellent. Controls feel a bit cheap compared to the OEM version, but that is obviously expected. There are pegs the go into the bottom of the camera to keep it from twisting.

This grip gives 9 FPS on the D850 with the following:

Wasabi EN-EL18 10.8v (the voltage increase over the OEM EN-EL15 is needed for the 9fps)
Wasabi MH-26 charger for Nikon EL-EL18 batteries
DSTE BL-5 battery cover (any BL-5 should work).

Tested on firmware 1.00 and 1.01 with no issues achieving 9fps. Total cost is a fraction of the OEM parts. Highly recommend.

Nice quality. I see no difference between this and the official Nikon grip I previously purchased for my D500. Comes with holder for standard EN-EL15a battery. This, however, did not increase my D850 to 9fps. I purchased the BL-5 battery chamber and an official Nikon EN-EL18b battery which did give me my 9fps.

For me, probably even more important than the extra speed in image capture is the field report from Mark Smith in which he found a significant increase in AF hit rate with this set-up. Since this camera is to solve the slow AF performance of my D750, I want all the advancement I can get. So far it's proven itself magical. Albeit, a heavy camera to lug around for sure. Worth it

Well the first on I purchased worked fine with the D850 giving 9fps but after about a week it stopped accommodating 9fps and went back to 7fps. I returned it and received a second one today. Excited to see how it worked, I connected it to the camera, installed the EN-EL18 and nothing. The camera at first wouldn't come on and after reinstalling a couple of times, the camera came on but it wouldn't recognize the EN-EL8 battery at all, Tried several times with two different batteries and the same result. So needless to say, I just returned it again. Not sure what I'm going to do, the Nikon grip is a ridiculous price but I imagine it works. Nikon is just getting greedy for a piece of plastic with a small amount of electronics.

3/6/2018 - This is a follow up to my earlier review. As I said, I purchased two and had to return both for various reasons. I received my third one two days ago. Third times a charm. This one connected firmly, the switches and buttons work pretty well, not as smooth as the Nikon, but acceptable, and I have been getting 9 fps. I have been on a few shoots with no problems. This is the first battery grip I have owned and with my missing some fingers, this is extremely helpful holding the camera in both landscape and portrait. My only concern is how long it will keep working at 9 fps, but at $60, I am willing to give it a try. I am also using the Wasabi EN-EL18 batteries. I have two, and both work perfectly. At first I thought it was the batteries, but it turned out to be the grip. On a side note, the Customer Support at Wasabi(Blue Nook) is exceptional. I corresponded with a gentleman named Terry and he was more than willing to help me solve this problem. Hats off to Terry at Wasabi (Blue Nook).

3/12/2018 - I've been using the grip for a while now and for the most part, it works fine. I get the 9 fps and can operated the camera.
The sub-command and main command dials don't work as nicely as the Nikon camera dials. They are slightly more recessed and they don't appear to have as nice a feel as the Nikon. They also don't have that distinct "click" when rotating the dials. My finger has slipped a couple of times because the notches aren't as deep it seems. Also, I took my grip off to charge the camera battery and when I reinstalled the grip, the camera wouldn't come on. I loosened it and re-tightened it and then it worked. It appears that the quality of the connection and the dials is where they cut costs. If I wanted to pay the absurd prices Nikon is charging for their accessories for the grip, I would get it for peace of mind. But it is out of my price range, philosophically speaking. If the Nikon ever goes down in price or goes on sale, I may get it then. But until then, this will have to do.