The Ec-S screen provides a much better manual focusing experience *if you are using fast lenses.* It also does a better job of showing actual DOF.
Fully agree. It makes manual focusing much more accurate, and it adds another visual feedback confirmation with AF. DOF can be seen much more accurately, especially at wider than f/2.8 apertures.
If you are using f/2.8 zooms, it's darker than the standard screen. If you are using anything slower, it's much darker. If you want to focus the f/1.2 and f/1.4 primes, it's great. Otherwise, not so much.
While darker, I also use it to focus my f3.5 TS-E lenses (which really require Live View for tilted focusing anyway).