To customer service, second only to sizing are questions on which shoe for which distance.
This is quite difficult to answer on its own, as it comes down to simple personal preferences.
To someone who has never worn Form before, the answer to "Is the Form a good shoe for marathons" primarily comes down to:
1. What shoes have you been doing your long runs in?
That's generally going to be your marathon shoe.
2. Is that shoe more similar or more dissimilar to Form?
You may want to go with one ...