I dont have one yet, I have the Logitech original case for Ipad 12.9, I have tried the new one in store with my 12.9 pro, I so much prefer it to the current case, it is so much slicker to me, you can adjust the angle, fold the keyboard for less space, it looks amazing also with the space grey ipad 12.9.
I have no idea if it will mark it, but I will be buying this case for sure this week in anticipation of me being able to buy the new SG WIFI 12.9 pro in the next week or so when they come back into stock.
I use my first gen 12.9 silicon back and Smart Keyboard for my new 2017 model, but noticed the back case has a split in it. I was amazed to find Apple don't sell these back covers anymore. Very strange decision IMO.