Sorry, I just saw there was interest in this. They were able to get everything off of an older iPhone, i think two generations prior to now, (i'm sorry I can't remember the exact model) but for updated (current) iPhones they were not able to get a full disk image, but could get "some" data. (I'm sorry I again can't give specifics as I don't remember, but it would be metadata). Essentially we were told Greykey keeps updating the software to find new ways to extract the data. We were also told it didn't work if the phone had been powered off. For the phones that it did work on, it extracted everything from the disk and then Cellbrite went through the data to present it to the user.
The Greykey device plugs into the phone, requires the phone to not have been powered off. The untrusted USB settings also help prevent it from working.