I bought a DSTE Battery Grip for the D850, a fraction of the price of a Nikon grip and it seems to be built very well. Close fitting, all the buttons work as they should. I have a generic battery on the way, it will be interesting to see if I can get 9fps with the DSTE grip and a generic battery (TBH I'm not that fussed over getting 9fps).

Time will tell if it lasts.