If I were a spook, it's definitely a technique I'd try (the FBI has run honeypots before). But other commenters have mentioned that it's run by a reputable grou

If I were a spook, it's definitely a technique I'd try (the FBI has run honeypots before). But other commenters have mentioned that it's run by a reputable group, so it's probably not a massive concern (then again we know that intelligence sharing occurs between the NSA and other agencies -- if I were ICE I'd ask the NSA to get information about the users of the app). I do imagine there is some legal red tape to get around if you actually want to use it as evidence in immigration investigations. Then again, you don't need to use it as evidence -- all you need is a lead and you can get all the evidence necessary when you detain them.