Although true in general that HVAC manufacturers can be sceptical of installing third party devices, it is quite commonplace to install start assist devices in HVAC units. Other typical examples would be drives and hard-start kits. Over the past 5 years, it has become an accepted industry standard to install soft-starters in AC/heat pump units to overcome the limitations of residential solar/battery backup.
Our product range has been associated with many after-market installations over the past 20 years. Since SureStart is aimed to enhance the life of the compressor, we have never encountered any case where the manufacturer has voided warranty for use of start assist devices.