No problem seeing a screen that's very close to you so that's not an issue unless both the driver and co-pilot want to watch the routing. You can use 2 phone if you like!
I have never seen any issues with my phone battery as it is plugged in while driving and it's still 100% when I arrive.
If you have never seen a phone that would give you speed limit info and warn you about it then you have never seen the WAZE app it does all of that.
GPS units have 2 be updated quarterly to even be somewhat up-to-date. Most of the maps can be as much as a year behind. I have watched closed roads open and Google have the correct information automatically in a few days.
NO stand-alone GPS has the traffic information available from Google and WAZE (both owned by Google) everywhere you travel and that's has saved by butt twice in my last 2 trips!