Depends on how much the devices cost to procure, and the budget of the party using them. Seems like these could be treated as "black-throws" given the right cost:budget ratio.
OpenBTS and Ettus USPR (software defined radios) have made it inexpensive enough for hobbyists to set up cellular base stations at Burningman.
The difference between an open source base station, and a homebuilt stingray in negligible.
While a grand or two's worth of radio hardware and however many weekends/evenings spent getting it all set up and the a software configured is _kind of_ expensive - it's effectively free at criminal org, corporate espionage, or state levels of action.
Not even that, if you want to use them as a MitM just broadcast the data you want and any arbitrary receiver will pick them up that can't be pinpointed.
That's assuming you don't mind losing the transmitting hardware.
For example an imsi catcher spliced into 120vac power and stuffed up into a ceiling tile in a busy shopping mall. I bet that with a stepladder, a clipboard and two guys in high visibility vests, a set of electrician tools, you could do this at nearly any mall in America.
One option might be to have the sniffing device setup with a hidden wireless network (of some sort).
Then when you walk around, sit in the food court eating, or if the device is close to the outside, sit somewhere out of sight of the cameras with a strong wifi antennae and grab whatever data.
Unless they have some "free" wifi that the device could hop on to send it to some server somewhere.
Using that and / or 4g would make it easier to find the device and, of course, the person though.
