Redundancy, Reliability, and Maintenance
With 6 floats we could change one while in the water. This makes maintenance easier. We could also lose one without sinking.
So less chance of sinking.
We will have 2 thrusters on each side. If one breaks we can still turn and go forward, but not as fast. We won't be able to
control pitch as well if we lose a thruster. But losing one is not a crisis situation.
We can carry a spare thruster as well. If we have a spare and one broke we could choose to replace the broken one, or continue on slowly.