Trickiest part is that the specialist aftermarket companies really want your business. Which means they can often offer you "more" than a bulk kit manufacturer (who is trying to balance cost to put a kit out across the entire spectrum of potential buyers, the better to increase sales).
"All in one box" is more convenient for the modeler, obviously, but may not always be an ideal choice.
Part of that is in the nature of ship modeling. Ships tend to be very specific, and will have specific details. And the differences are often visible, too. Which means they matter.
Gun turrets with one "knuckle" versus two; gun director houses with flat or angled backs; specific superstructure shapes or configurations. So, even if a dozen of a given ship were made, each one of those can often be identified by features in photos.
And, just what (or which hull) the kit manufacturer modeled matters, too.
Trumpeter's 1/200 US carrier line exemplifies this latter. The one hull castign is meant to be Enterprise, Essex, Hornet, and Yorktown--Which are similar to each other, but much in the same way a Pzkfz IVA is similar to a IVG. If you know, you know.