The South Seas 860B is very similar to the Artesian Emerald we owned for ~17 years. The Emerald is basically the predecessor of the Island Grand Cayman, which is the sister of the 860B. Ours fit 6 adults no problem. The foot dome gives you a place to anchor your feet so you're not crossing legs with your fellow bathers. We liked it a lot and considered buying the same thing again, but wanted to go bigger this time.
Ours was relatively trouble free. The heater needed replacing somewhere around 10 years in. That was the only time we had to call for service. We also replaced a few of the headrests/pillows after they became a little bit ratty looking. Last summer, we decided to retire it due to frame rot. It was located in a damp area and did not have a sealed bottom, and we weren't always diligent about clearing snow & ice from around the skirt. Eventually the lumber got soft and started to attract carpenter ants. Artesian has since addressed that issue with an ABS bottom.
One concern I mentioned earlier is that full foam is optional on both spas you're considering. Unless you live in someplace warm like Florida or SoCal, I think it might be a mistake not to go with full foam. It also helps reduce the running noise and supports the plumbing.
