I have the new high-end 15" with dGPU. Since I am still in the first 14 days period, I have been experimenting with it a lot, looking for signs of trouble. Worked with Photoshop, Lightroom, did some video editing, quite a few hours of watching HD movies/videos, and little bit of gaming; I haven't seen any problems with the screen / GPU switching.
I also did do the screen calibration, and made a few changes to the profile; I seem to like D50 [warm yellowish white] more than the native white point settings - that was way too white for me.
Best,
Edit: Screen manufacturer is LG, and... as far as brightness goes, the VERY bright setting is actually... quite disturbing. I generally keep it around 1/3 way in.