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Rick, I'd be hard pressed to explain the difference as I've only made it with the ECA.
For me, going the ECA route was simpler than the starter culture (no fermentation time required). So using it can be a time-saver, especially on big batches.
I have discovered that ECA can tend to make some of the sausages I've made progressively more 'sour' the longer the meat sits. I'm not sure that is the case with starter cultures once there fermentation stops.