My cars been treated with a similar product when i worked for a franchise dealer, it definately isnt just a case of hosing the car off, especially at this time of the year! That said, it always comes up looking great after a good wash and the cordy has the best paint work out of all five of my VAG cars by a mile! I've found it needs topping up semi annually to keep it in full effect, however as i have a supply of the product and the knowledge to apply it its no cost to pay
TBH I didn't think a simple hose down would do the job, especially in winter as you say, so I invested in some good cleaning products which do the business...it just takes a little longer but its worth it...
You're topping up twice a year then...I guess if you can do that for free then its worth the effort...