Filter will remove some iron, but not all. Depending on how much iron you have it may be perfect.
Essentially, my water used to have a metalic taste to it, after running through a filter, it was much better.
I brewed with the filtered water and won many awards with my lagers and light ales...so I the answer is...they are both right.
The filter may remove enough you can brew with it, but it is not 100% effective... but it likely be effective enough.