I did a project with one 300HP SMC Flex on it last year and compared to most of the other soft starters out there I thought they had some issues that made them less desirable.
For one, I don't like their concept of 3 separate 1-pole bypass contactors. Cutler Hammer does this too and I think it's a waste. You are paying for that feature, but you CANNOT under any circumstances use that contactor configuration to start the motor in an emergency if the soft starter is down. I would rather put in my own contactor and have the choice by virtue of how I size the contactor.
For another thing, they apparently MUST have fuses in front of them per their UL listing, even if you already have a circuit breaker! That to me points to a design weakness.
I also had trouble with the fact that they are not very heavy duty; I used it on a rock crusher and lost one power pole the first time I turned it on. Mind you, I have been in the soft starter business for 20+ years so I know what I am doing, this was not "operator error". The SCRs just apparently could not take the 30 seconds at 450% current it took to wind up this crusher. Allen Bradley is very secretive of their SCR overload ratings and this has always made me suspicious.
The big eye opener for me was that the replacement power pole, ONE pole, for the new SMC Flex was more expensive than an entire 300HP soft starter chassis from several other sources! Granted, that power pole has the 1 pole bypass contactor built in and includes both SCRs, but that was ridiculous IMHO. The only good thing I'll say about it was that changing that pole was a breeze.
The SMC-3 (and SMC Delta) are not made by AB, they are made by Omron in Japan and brand-labeled by AB. These are very light duty soft starters, I would hesitate to use them on anything but a centrifugal pump or fan. They too cannot have their integral bypass used for emergency starting. They also have no snubbers on the SCRs, choosing instead to put a small warning in the manual that users should install their own varistors or line isolation contactor. This means, if you didn't happen to see that warning, normal line transients can cause your SCRs to self-commutate (turn on without being commanded to) and/or short.
My recommendation: Motortronics or Benshaw (or Toshiba which is Brand Labeled Motortronics). Both of them are heavy duty rated AND, importantly for refer compressors, they each have a feature that, if for some reason you short one SCR, you can defeat the Shorted SCR Lockout and restart if you have to with the remaining SCRs. The start will be rough, but you don't lose your refrigerated product while waiting for a $3000 power pole assembly to be flown in to you. I used to use that on fishing vessel refers after an AB old SMC died at sea and the user lost an entire hold full of salmon.
