Welcome to our forum.
The price you got on the J-355 is good, the J-375 to me is high. Jacuzzi owns Sundance so the are very similar construction wise, some will argue that the 800 series only matches up to the Jacuzzi 400 series for which I disagree. The 300 series Jacuzzi is a very nice spa with great jetting. As far as air goes both are similar as far as what comes out of the jet. The Sundance does offer the air blower which does nothing but add air to the spa through little holes here and there. Some like it some don't I personally don't care for it. Basically its vacuum cleaner on reverse. Value wise the 300 spa has a lot to offer. If you want to discuss further feel free to call me, 360) 424-4132 Don't mind at all