Bought the DSTE MB-D18RC grip off of eBay. $70 (make them an offer) includes the grip, two battery trays (EN-EL15 & 8-AA batteries) AND a remote control. Hence the "RC" I'm guessing.
Took three weeks to get to me but given that shipping was free, it was coming from China, Christmas season, Bomb Cyclone weather where it entered the US and then it had to be sent to the west coast all in all not too bad.
Bottomline everything works. All controls do what they are supposed to do. Shutter release is very good.
Little digression here. I had the DSTE grip for the D800.
They have improved the release from their D800 grip. Much more of a discernible feel between 1/2 shutter and tripping the shutter.
Control dials are smoother in texture than the previous grip so you have to put more force to get a grip on the dials when turning them.
Joystick Multi selector feels just like the one on the D850 body.
I have the DSTE EN-EL18 battery which has a permanently molded BL-5 adapter to let it work with the MB-D18. The great thing about this battery is that for $40 you get a EN-EL18 + BL-5 + Charger + Car Charger!
The chargers plug directly into the battery. You can even plug the charger into the battery without removing it from the grip. Never used the car charger so I have no idea how long it takes to fully charge the battery. Just good knowing it's there though.
All those naysayers and whiners moaning about how there is a ridiculous cost to get a grip onto the D850 with a EN-EL18 battery either just like to complain or haven't checked around enough. $40 bucks and you're in the game.
Plus, this D850 grip comes with a wireless remote! Just a simple push the button, camera takes a picture remote. No time-lapse or any other feature but still handy to have if you don't have a remote already. Works best in line of sight but will work around corners. Gives you a range of about 30ft.
Big question for a lot of folks is does it give you 9fps with the EN-EL18? Truth is I don't know. it sounds like it gives you a higher frame rate and over 5 seconds timed it did give a couple more frames than just the body alone. But did it give a definitive 9fps? I wouldn't stake my life on it.
Finally the build quality. Does it match the Nikon $400 MB-D18 in construction or materials used? No. It's plastic not magnesium. But in the whole scheme of things is that a deal breaker for you?
Look you can buy 6 of the DSTE grips for the same price of the Nikon grip. It fits tightly on the D850 without any rocking or wiggling. The rubberized part feels and looks the same as what's on the D850 body. Not to mention the remote control. Should the grip die at a critical moment, especially a paying job, that can be all sorts of bad. I used a DSTE grip on a D800 for 6-years and had no problems - ever. If this DSTE D850 grip works as well as the DSTE D800 grip I'm not going to worry about it failing. For me it's worth the risk to save a few buck and go with the DSTE grip. Your mileage may vary.
Bill F