My first work for them ever was actually a circuit of completely pre-security locations at the big airport nearest my home. Now I do both pre and post for them, they arrange a gate pass at the particular airport in question. I guess they may not have that ability at every airport.
From my experience working with them, they specialize in airports and shopping malls. They work with a number of operators of airport terminal 'shopping malls'. One of the good things is that you can grab a circuit of shops, which will make a day of it, and the money they pay is competitive. Granted, getting a number of emails about open locations at airports across the country isn't the best, but then again, if I am travelling, and able to pick up a filler while walking through an airport is a pretty good thing.
Philadelphia Based, covering Eastern Pennsylvania, Delaware, New Jersey, Maryland