With regular departures and being completely free I was very impressed by the SIF. The views back to the skylines are great, and you get a good view of the Statue of Liberty without having to pay for one of the specific tours.
The journey takes under 30 mins and if you are quick you can make it on a ferry that returns within minutes - so it wont eat into much of your day.
We were luck to get two different style of boats during our round trip - the first which had open sides you could walk along and get great photos. The second was fully enclosed so you would have to take photos through the glass - try and get the former for better shots and a better experience!