I have the Progressive EMS-HW30C and have been happy with it. I do not have a transfer switch, just a generator out receptacle that you plug the shore cord into. I wired the shore cord into the EMS so it protects from either shore power or the generator. It works fine and I have not had any issues with it. I like the remote indicator, as I am always looking at voltage as A/C, microwave, and water heater are used (microwave and water heater share a circuit with a priority box that allows the microwave to run and shuts off the water heater. When microwave stops, water heater gets it power back.)
I am a technical person, so being able to see the volts, amps and cycles is nice. The long delay is 136 seconds. Some new A/C units have time delays built into them, and if yours does, you can go with the short delay.
Charles