I'm getting mine undercoated tomorrow. Rust starts immediately on certain things under there (anything not painted, and anywhere plastic clips scratch the surface off like the lines and such)
Just be careful to get a shop to do it that uses the proper stuff. A lot of the cheap sprays will cause ALL the rubber seals to swell and expand.
I'm getting Ziebart to do mine, with their 'sound shield' coating as well.
as for the module, they're getting away from the typical 'sacrificial anode' type, as those only work on something that's submerged in salt water all the time.. the theory behind the new ones is that it reacts with the zinc plating if you get a scratch and eats that away instead of forming rust on the steel. sort of turns the galvanizing into a sacrificial anode.... but still, the only thing that actually works in the box is the flashing LED. until that fails.