As a backer, I got mine already at the photokina.
It just works fine. I got the N1 version (I tested it with D200, D810, D4, D850, all with the round 10 pin socket). It comes with two little cables to connect it further with the USB socket (2 cables for 2 different USB sockets).
I use it with my apple phone (so far it seems Apple has restricted the download to phones, could not find the software for iPads, though in principle it should work there).
The connection with the USB port is needed for getting exposure settings and for downloading the picture (a small version) into the app. As it is a small picture, it works with the D850 also fine (no extensive waiting). When the phone went into sleeping mode, it takes about one or two seconds to reconnect, then it works instantly. If something does not seem to work, it is related to the settings on the camera (e.g. it seemed Af was not working, but that was due to my settings on the cameras).
After slightly more than a day, the reconnection did not seem to work. I guess this is due to some settings on the phone. I simply had to de-connect the little item and re-connect it again, then everything was fine again. Also the GPS-data from the phone get into the picture-file. It still recognises some cameras wrongly, but that is already known to foolography and it does not impact the functionality of the tool (they just did not have all cameras to read out the correct IDs).