Why its hexagonal? The practical reason is that it can fit more people in the barrel. A barrel with a diameter of 188 cm can seat up to 7 people comfortably. Not so practical reason is the design. Hot tubs are classically round-shaped. We have clients who are always looking for different and fresh looking solutions.
Why to prefer external heater? It’s easier to fire-up and also easier to clean. However, it also needs for more space to install.