The added weight of a bidon cage with a protective coating may seem insignificant, but it can add up over long distances and demanding races. However, I agree that the benefits of such protection might be overstated and could indeed be a marketing gimmick.
I'm yet to see any compelling real-world data or experiences that support the superiority of these coated cages over their simpler, more cost-effective counterparts like stainless steel or titanium cages. As a cycling aficionado, I'm inclined to think that the real issue of corrosion or abrasion is more dependent on the protective measures taken during storage, handling, and racing conditions.
Let's face it; the majority of cyclists don't need these high-end amenities, as failures in bidon cages are quite rare in our day-to-day experiences. While it is essential to address and prevent such instances, I believe the solution lies more in adopting good practices and equipment maintenance regimes, rather than relying on fancy protective coatings.
In the end, the choice of cage and protective coating will depend on individual preferences, resources, and racing demands. Still, the cycling industry should always be held accountable for truly delivering performance-enhancing features rather than riding the wave of unsubstantiated marketing claims.