There used to be issues with external monitor flicker in the xps 15 but they were solved some time ago, the only issues I know of that remain (and they drive me crazy) is connecting external displays through a usb-c dock (such as the dell TB15) - but at least in my case it's not so bad.

Trackpad is excellent - responsive and smooth. two finger scroll, pinch to zoom and just normal delay and sensitivity is great. Not sure what more one needs (I don't use 3 or 4 fingers really).

Never had coil whine.