I have a KF v.1 that I used for reading books with photos, maps, etc. - stuff that didn't display well on my KF3 Keyboard (which was my default ereader) or on the DXG. I also used the KF for reading magazines.
The KF HD screen is a vast improvement over the KF v.1. It is brighter, crisper, clearer, etc. - and ScreenDim is now available for it.
An odd note - one of the magazines I read regularly is the NYT Book Review. On the KF v.1 the table of contents was displayed on a black background. On the KF HD, there is a white background.
After using the KF HD, going back to the KF v.1 - the screen looks dark & "dingy" to my eye - I am definitely staying with the KF HD. Subjectively, it seems much easier on my eyes when reading for long periods of time - and my eyes are VERY sensitive to light.