Re: Value?
The iPad Pro runs iOS not Mac OS. Which means no mouse pointer on screen, no need for a trackpad.
It's really no different from Android devices that don't show a cursor on-screen until you attach a mouse to drive it ... except that with an Android device you can attach a mouse to drive it.
(...but I see I'm not the first to point that out.)
My Sony smartphone does look a bit odd with an OTG adaptor and a Microsoft optical mouse attached (and I bet the mouse's LED sucks the battery) but I do get an onscreen pointer, even on a phone!