Actually the size increase is more significant, IMO than the brightness increase.
If you hold both up to your eyes (turning the cameras in opposite directions to get them vertical) you can view the world in a sort of [DF+ / XF] Binocular configuration. Holding them like this lets you make very easy direct comparison. It also makes you look rather dorky (will post a picture later for full self depreciating experience).
The XF Viewfinder is:
- slightly brighter
- slightly less warming (more accurate)
- a good deal larger
- detachable (allowing WLF option)
- moderately heavier
- more specific in showing the AF area*
Whether you can focus manually is something I'd rather leave to you to test for yourself as a great deal depends on your eyes, your normal working distance to the subject, and your typical working apertures. But yes, the increased size of the viewfinder should provide a better tool for manually focusing.
*Notably the currently shipping XF bodies do
not have the new ground glass, but will receive them when they are ready. The final shipping ground glass has two rectangles, both smaller than the circle shown in the DF+ ground glass, and the smaller of which is quite tiny. They represent the average and spot focus areas respectively. I played with an XF with this new ground glass in Copenhagen and it is, in my opinion, a big improvement as far as indicating to the user exactly what the AF sensor is looking at. But we'll have to wait until that final ground glass starts shipping to get wider (less biased) opinions.
Update: here's a photo of us testing it:
https://instagram.com/p/5PtQ4ri51K/?taken-by=digitaltransitions