So this freshwater salt system was just added to tubs for this 2019 year model. From what i understand talking to my dealer - they refused to sell the older ACE system because it was so terrible. As one of the larger more established dealers, they helped HotSpring beta-test this new salt system for much longer behind the scenes and in their showroom before the system was finalized and released to the public.
When researching and deciding between the two options, I learned that the Freshwater salt systems can be tricky to "start up" - once the system is balanced your system will not have a problem keeping up with the chlorine generation needs. However since it's a new spa you are going to need much more sanitizer than normal. Far more than your spa can produce on it's own. My dealer stated they include a whole gallon of bleach with ever new Salt system to help customers get the system going initially.
I personally opted not to have the Freshwater Salt system installed on my spa, but I like knowing it's cheap enough if I wanted my dealer to switch me over from one system to the other. For now I'm very happy with my Ozonator system, cleaning and maintenance has been a breeze