I tried a coating on the 54" deck of my x595 last summer. It is a graphite loaded acrylic that is quite resilient. The intent is to prevent the cuttings, which are usually a mixture of grass, dirt, and moisture, from forming a tough build-up. This crud can be really hard to remove. Long-term, it accelerates the rusting of the deck.
Anyway, the coating works well, but gets worn off by cuttings, sticks, rocks, etc from the very areas you want protected the most.
Power-washer -- haven't tried that yet.
jim