Smidey - you can do a search on HH vs HD steel or similar to find out much more info, but in a nutshell, the HH is a full stainless steel and HD is semi-stainless. Many experts here prefer the sharpening characteristics and edge retention of Kono's HD steel. As long as you don't let water sit on it for a LONG time, they're almost stainless with normal maintenance. Just clean and dry after a round of use. If you want the knife to sit all day, unattended, then HH might be the ticket.
Professionals regularly use these knives as their all purpose tools, using good technique, given the thin blade. They aren't delicate, but they aren't Western Deba's either
. If you do well using your Moritaka w/o any or little chipping or damage, you should be just fine with the Kono.
If you decide the Kono HD 240 Funy/Gyuto (not in stock) is the one for you, someone in the classifieds forum posted a want to trade on this knife for a normal Kono HD 240 Gyuto (which is in stock). You might check that out and see if this might be an option.