How much are they charging? If it sounds to good to be true......
Save your money do it yourself.
Just what I do,
apply once a year, it shines well, lasts and makes washing much easier, it protects but won't stop the filiform. In my experience nothing has stopped it on Airstream panels.
A consistent maintenance program is the best way to control the corrosion, no matter the product used.
Our new areas of corrosion slowed dramatically after about three seasons, as of last Fall no new areas.
It helps to know
...what your dealing with.
Do the google
try to get thru it anyway.
Others may disagree but it werks for me