The downside is the following clause:
Smart thermostats also allow Con Edison to remotely adjust the amount of electricity your central air-conditioning system uses to help reduce the demand for energy. A signal similar to a pager and/or beeper will communicate with your central air-conditioning thermostat and will cycle your unit’s compressor on and off to reduce demand on our electric system.
That means they can shut off your A/C whenever they want. You wouldn’t want that to happen on Shabbos, and imagine if they shut it off at the beginning of a three day yom tov!