A lot of it comes down to knowing which armor features come from which film in the trilogy. As was mentioned above, there is a conglomerate of different smaller details that are specific to an individual movie that are occurring within the Disney armor.
For example the soles of the boots are black in ANH and ESB, but are white in ROTJ. So if the Disney armor has the white soled boots and the trim on the armor, then it most likely represents the armor in ROTJ, which would mean that the frown should be painted black and not grey.
Although the helmet does have it's quirks, I will admit that it is better than the FX helmet that most of the 501st troopers wear when marching in the parade!
Here is an accurate helmet for reference:
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The Disney helmet could be improved by:
-smaller, blue tube stripes
-more accurate mic tips
-grey cheek traps instead of black
-3 screws added to each ear (if they aren't already there)
-perhaps make the eye opening bigger/wider (this can only help the people in costume also be able to see more)
As for the armor, besides what has already been mentioned above:
-the drop boxes should be hung with white straps not black
-Holsters? It would be great to see some leather holsters riveted to the belt!