Are all three phase soft starters the same?

No. There are different styles of soft starter which control the motor in different ways and offer different features.
Single phase control
These devices reduce torque shock at start but do not reduce start current. Also known as torque controllers, these devices must be used in conjunction with a direct on-line starter.

Two phase control
These devices eliminate torque transients and reduce motor start current. The uncontrolled phase has slightly higher current than the two controlled phases during motor starting. They are suitable for all but severe loads.

Three phase control
These devices control all three phases, providing the optimum in soft start control. Three phase control should be used for severe starting situations.