Soft Start, Easy Start, Quick Start, Sure Start - all have the same purpose, but manufacturers use their brand name for it. All of them working similar by reducing the voltage during starting to limit the max ampere draw while trying to maintain a high torque.
Each manufacturer has its own technical approach to solve this tricky task. No question - some brilliant engineers are involved in the design of this sophisticated device.
These devices are highly complicated electronics which makes them significantly more expensive than the traditional hard start kit.
Pros: They got a lot of positive feedback and are very reliable. A good choice if you have a small size portable generator to power your RV or Boat Air Conditioner.
Cons: Expensive! Probably needs an electrician for some rather difficult wiring modifications and installation. Some air conditioners have to be converted if they incorporate a Triac switch.