Having used a HHKB, the arrow keys and page/home keys are aggravating to have to chord when you are in a program where you can't remap to the expected key combinations (and the chords all have to be done with just the right hand, unless you want to give up your CMD/Windows key).

The swap of del and '\' is annoying too, and creates problematic muscle memory that will fail you when you're forced to use a normal keyboard.