The HHKB feels and is lighter than a Realforce, not only due to the size difference but also due to the former's plastic plate versus the latter's metal. That being said, the overall quality between the two is largely the same. They're both incredibly solid. From a typing perspective, I prefer the feel of the HHKB, particularly the Type-S, over the Realforce.
I'm not sure how the HHKB would be for Photoshop use, but a good compromise might be to seek a Leopold FC660C since it has dedicated arrow and other keys, plus you can use a dip switch to swap caps lock with control.
For straight typing, which is my primary use, the HHKB is awesome.