I finally bought one. It’s one of the best purchases I’ve ever made. i actually like it much better than my Wacom 27 QHD. I use it for everything.
Yes if the screen has a lot of oils on the surface it will feel slippery.
However the whole reason why I purchased it was because when I tested it in the store, the Apple pencil dragged on the screen the way the Wacom pen would not. I do not use a screen protector on the ipad pro.
I do use a screen protector on the Cinitq. I actually rub a kneeded eraser on the Wacon screen to make the pen drag more.
Of course everyone is different. Go to the Apple store and test it. Understanding that dozen’s of people have touched it with oil’s all over their skin. It will be slippery.
I love it.