There is not a distance that is good or bad to focus at.
Having little variance in focus distance throughout the day (long or short) can be bad, while focusing to either end of your visual limits can be tiring.
That's not what I mean. I mean the display inside the lens would require a radically different focal distance (it's less than a millimetre from the lens) than the world outside (where you would view between 20cm and infinity). I don't really see how they could consolidate that within one lens.
It's actually impossible to focus on an image within the lens, sort of by definition. It said the display is holographic, which I guess means that it will diffract light to create the appearance of an image at infinity, while not actually making an image in the traditional optics sense.
Having little variance in focus distance throughout the day (long or short) can be bad, while focusing to either end of your visual limits can be tiring.