I got mine, works with the GFGT well, force feedback and all. My laps times are abysmal right now but I just need to get used to a wheel again. I had a heck of a time updating the firmware though.
Soooo, for future reference, before putting the converter in your PS4, put it in your computer. and you have to update it.
Go to
www.brookaccessory.com/download/, find the proper PS3-PS4 link. (updates will be a .exe file in a zip archive)
***You'll have to go to the very bottom of the list, open that google drive link first*** and download that update there, v1.7 I believe, before you try downloading any from the list. That's the part that had me frustrated, there is really no proper instruction on Brook's site.
The light on the Converter stick should turn purple after it's done.
There is also 2 updates called something like "PS3-PS4 steering wheel update", one works one doesn't. I think I had success with the link closest to the bottom of the list, but no harm in trying both.
If the update was successful the .exe will say so and the light on the converter should turn from purple back to it's original blue.