Kinda depends on what you want to achieve or assess.
If you want an enjoyable day at the range for some live-fire fun, using your gear, go with the IDPA event.
If you think there's something you need to have assessed regarding your close quarters skillset, awareness and decision-making, and you're in good physical condition - and the FoF is being done by a reputable and experienced instructor(s) and company - go for the FoF session.
Personally, I'm of an age (hitting mid 60's) where I've already had the opportunities to have the "what are you gonna
do?" questions answered to my satisfaction, regarding both martial arts and shooting/tactics/fighting skills, and I'm content to just keep working on trying to fight off the ravages of aging.
I'm not someone who enjoys competition for the sheer enjoyment of competition, but if faced with having to choose between only those two options, I'd go for the IDPA afternoon.
So, what do
you think you want to do, for whatever reasons make the most sense to
you?
Which one will mean you have to
clean a gun at the end of the day?
(The armorer in me means gun cleaning stopped being a relaxing diversion many years ago, and became just another chore - which is what happens when you've had to clean so many guns neglected or abused by innumerable other people.)
Which is closer and costs less, and will leave you in a sufficiently mellow, relaxed condition to enjoy an adult beverage at the end of the day?