I bought a DSTE D850 grip, a DSTE MH-26A battery charger, a DSTE BL-5 Battery Chamber cover and a generic En-EL18a battery all off eBay.
Happy to report that the D850 sings along at 9fps for a fraction of the price of buying Nikon products.
The grip is well made, I haven't ever had a Nikon OEM grip before, but I have had OEM Canon grips for a 50D and 5DMKII and the DSTE grip is right there in quality.
You can definitely hear the difference between 7fps and 9fps.
You really do need a XQD card so that the buffer doesn't fill up quickly.