First, let me say I've never been to IOM.
That said, I have talked to numerous people who have gone there to do family research, etc.
With all of the computer info, help from fellow researchers, etc. one can get a lot of significant information BEFORE the trip.
Then the time available on the trip can be used to soak up the culture, atmosphere of IOM, see where family lived, etc. The time can be used to look at records that aren't available elsewhere and need to be done there.
i.e. it would seem advisable to do as much ahead of time as possible and then see where the gaps are.
You may be surprised at how much info you can get right here.
Let us know who you are researching--names, dates or time periods, etc.
Donna