EZ Starts are very easy to install.
This plug in unit looks like it might be a power factor correction device Those are good too but I'm not sure they would qualify as an Easy Start.
I've used them with some hardware (A dehumidifier) and it made a significant improvement in the unit's overall power needs.. A re-charge helped it to work better too (This is a refrigeration device like an air conditioner) back then you could by what you need to make it rechargeable at a hardware.
But will it work for "Soft Start".. Well.. Perhaps a little..
(The PF-correcors work by adjusting voltage to bring Voltage and current into phase.. Normally on a Motor (like an air conditioner) ELI the ICE man plays havoc with the relationship between Voltage and Current (ELI Voltage Leads on an Inductive load) so the correction device lowers the voltage or it can add some ICE (Current leads in a Capacitive load) Or Capacitance.
I do have a 2nd hand story about that.