Infil/Exfil is a quick supplement that adds some extra charm to the start and end of your FIST missions.
The PDF is 2 pages, with a nice technical manual feel to its pamphlet layout. Everything is cleanly organized and easy to read.
Contents-wise, there's a range of different types of infiltration and exfiltration options, but they ultimately boil down to a dice roll to see if something goes wrong. And statistically, something usually goes wrong.
None of the complications are so severe that that they'll kill characters outright, but they can put the squad in difficult situations or force hard choices. And for exfiltrations, they can require the operatives to have a backup plan.
I think my only quibble with Infil/Exfil is that it seems like with a little bit of bad luck, it's easy to get stuck in a loop of multiple failed exfiltrations. To that end, it might make more sense to only roll for a consequence on an exfiltration if the exfiltration is hot.
Overall, this is a really neat add-on for any game of FIST. It keeps the entry and exit points for missions nice and dynamic, and adds some extra tactical flair to a game that revels in precisely that.