I own a D1 Nautilus. Great spa, easy to maintain, excellent therapeutic results. To answer your question about chlorine use, my wife and I soak for 20-30 minutes every day. I use 2 tbsp of mps after each use. I use 1 tbsp dichlor every 3-5 days. My water is crystal clear and clean. I don't think you can go wrong with either of your 2 choices. I am very happy with my D1 however Sundance makes a quality product as well.