I would be curious to know if there has been legitimate success with this system.
and that's where the problem comes in, lots of claims from the manufacturers (rather a biased source I think)
and a few claims from eager people who note their vehicle hasn't rusted out from under them in the 2 months they've had the system... but I have yet to find any long term study, or unbiased source confirming that they work.
Cathodic protection is great, but on a car.... I'd love to see some proof.
Best bet for now is some good undersealing, keeping the vehicle clean, and making sure any rust that does exist gets dealt with immediately.