I can't speak to the comparison because I've only done one...
I put the soft start kit on our Axis (we have the 13.5k A/C). So far it has been working as advertised:
- The compressor ramps up in speed when the A/C first starts--no longer hear the "thud" as it kicks on
- I have an ammeter installed and see the current ramp up slowly to the running current (around 12 amps)
- I have now successfully ran our A/C for long periods of time on our 15a garage circuit
Oh yeah video, I did take video of the ramp up...let me find it
here it is: