Hi Tim,
The A21N profile was extrapolated from the A20N, which itself is already based on very limited data. Hence the “Fair” label.
I haven’t actually tested it with any add-ons in particular, so I can’t really answer your question. My instinct would be that if you have already tweaked the A321 profile to match the add-on you are using, that will probably be more accurate.
The true A21N profile might have an edge in situations where you are intentionally flying below the optimum altitude, for example. But I would say that if you are happy with the accuracy of your tweaked A321, just keep using it!
Best regards,