This would make sense if not for the claim that they list the same drivers as the replacement part for both models. Or do they when picking up the order do the testing to see if it's a 595 or 555 part?
Well it could be that the replacements are substandard, I mean otherwise they'd have to be a matched pair. And if you damaged one, who knows what shape the other one is in.
But I'm willing to bet that at the lower end it's not worth the end. These aren't studio grade.
It’s hard to make electronics that are identical. It’s easier to make them such that they fit within buckets of tolerances.
Without proper testing, it’s hard to know for certain