I have the Micro-Aire Easy Start. Jrref is correct. A hard start pushes more current to help an aging motor/compressor start which isn't good on the motor/compressor but if it will allow you to get by another few months or a year then it puts off the ultimate replacement cost of a new AC. It isn't good for a relatively new unit as high current can/will damage a motor/compressor. Will either save you money on electric costs - No. It will reduce the current to start the AC and will reduce the startup clunk noise. It may save money on helping your unit last longer and not have to be replaced sooner. My AC went from a startup current of 79 amps to 26 amps.
Check out the info on the easy start page.
Easy Start Soft Starter