Yes, I installed one on my Carrier 2.5-ton unit for two reasons.
1: So I could easily power the A/C with a portable generator.
2: To reduce the startup noise of the unit.
My unit was very loud at startup and it made sense to me if it could be started with a lower current then hopefully this would extend the life of the compressor.
I've been running it for about a year and see no negative impact.
EasyStart™ Flex: Soft Start AC Home Starter
– Micro-Air, LLC