The only thing I have against the top IPS, bottom TN setup is that on top of the difference in quality being jarring, the IPS and TN screens are inexplicably set to different color temperatures very often, so the end result is often that you get a bluish top screen and a yellowish bottom screen.
I don't know why nobody in the press has made a stink about this because it really really sucks that Nintendo does this.
Here's an example of what I'm talking about:
http://i.imgur.com/Zy1gjh1.jpg
Not mine but my Majora's N3DS XL has this same issue but not quite as prominent.