Conflicting info about how to use a normal map in Cycles

On his youtube channel, Andrew Price has the video “The Secrets of Realistic Texturing in Blender”, where he adds a normal map to the material output’s displacement input.

That may not be the correct way of doing it according to this other guy.
This guy stresses that it’s important to not mismatch data types. So he says the correct thing would be to put the normal map node output into the diffuse shader’s normal input, so you’ll keep all the normal map’s information. Also to mark the normal map image texture node as “non-color data”. He says applying it to the displacement can sometimes work, but the best way is the normal input.

So who’s right? What’s the correct way?

So who’s right?
The ‘other’ guy is correct using the’Normal Map’ node (I guess the clue is in its name)

If you go to the link in the blenderguru youtube description you’ll see he has corrected his error