I only know as much as I gleaned from that ad, but can't that it would really help, except possibly palliatively. 'Navicular syndrome' is a whole hoof problem & damage to the navicular bone & region is just one of the more obvious results. Toe first landings cause the main damage.
Enabling the horse to *comfortably* use it's heels correctly & therefore build strength in them, is the basic 'fix', although palliative(& generally short lived) treatments such as eggbar shoes & jacking up heels(therefore forcing toe first landings even more) are still common. Check out barehoofcare.com for one of many good sources of info on how to manage/rehab the horse. There are many reasons for horses not to be comfortable using their heels properly, ranging from simply lack of development, living on soft ground, being over shod, especially before maturity, working on surfaces the horse isn't 'conditioned' for, thrush, bad mechanics...
It could just be heel pain he's having rather than navicular.
The common reason for diagnosis, according to common definition in these parts a, it least, is indeed (otherwise)unexplained heel pain. 'Navicular syndrome' effectively just means unexplained heel pain. 'Navicular disease' however is diagnosed from rads that show damage to the navicular bone &/or surrounding tendons & ligs. Regardless the cause of the heel pain, it's best not to wait for the resulting bone damage before addressing it.