The buttons look like they are mounted on the circuit board, vs. being a daughter board of some kind. I think you would have a hard time getting an installer to mount the LCD and the buttons in a useful position.
This looks more like a DIY project.
You could mount the LCD in the Double Din opening behind the existing bezel of your dash. Then wire some momentary switches remotely from the circuit board to your dash.
The circuit board is larger than the screen itself (north and south) but smaller (east and west) in the width. It really depends on your car and how much room you have behind the dash.
AS for the brightness, I would wonder if the 400 rating is before the TS overlay is added. The overlay seems to reduce the brightness by 100 as far as I can tell.
I think they are both the same setup, one just comes assembled, the other does not.
Either way, it shouldn't be a whole heck of a lot of work IF you have the space in your dash.
Hope I helped....