I have a WaterFurnace ATV034A110CRT, from the serial (JG3570), I estimate it is about 31 years old.  I bought it new when I built the house.  It has been a great unit, still works well.  After a recent power outage I became curious about adding a soft start to allow me to run the unit on a generator if needed.  I see WaterFurnace makes Intellistart (or relabels it), and there are many other soft starts marketed for use on a compressor.  Is there any downside to adding a soft start to this unit?  Some reading mentions use on scroll compressors, the age of this compressor leads me to think it may be a piston style, but not really sure.  I would think it would help extend the already long life of this compressor for a minimum investment.  Thoughts???

https://www.microair.net/collections/easystart-soft-starters/products/easystart-364-3-ton-single-phase-soft-starter-for-air-conditioners

This is what it said about reciprocating style on the Hyper Engineering web site:
Reciprocating & Rotary Compressors SureStart technology can be applied to most reciprocating and rotary compressors as long as they fall within the correct range of Full Load amperage
rating of the listed models. Systems using these types of compressors must equalize differential pressure across the compressor during off cycle. SureStart is not intended to start compressors that are under a large differential pressure at startup. Doing so will compromise the life of the SureStart.

Well here is my experience... Started down this path back in 2014 wanting to run my 4-ton Hydron Module heat pump during extended power outages.
My Running Load Amps is 15A in Stage 1 and 21A in Stage 2. My Hydron mdl H50 has the LRA spec at 120A.
No way my Onan 7.5kW diesel genset going to start the GHP.

Doing the research and found Hyper Engineering's SureStart. They OEM SureStart to all the major HVAC mfg.
At the time Copeland was promoting the HyperEng 'Surestart' as Copeland 'SecureStart' and have a buy one at $300 and get second for free special.

If you are electrical handy, not hard to install. Recommend buy a compressor electrical pigtail so it makes the install easier.

Now when the generator is running and GHP compressor kicks in, the generator just grunt and pickup the load.

Last year installed a 12kW Enphase PV system with 'Solar Backup' and added on 5kW to buffer load if a cloud goes by.
Each Enphase 5kW will only discharge at 15A max so added another 5kW battery. With 10kW of battery now able to start GHP load.

Another bonus with SureStart is when the compressor kicks in no more lights blinking...

Bob G.