Intravenous drug use
While this technology might sound great for a needle drug user, there is one possible problem: How easy is it to undo the tourniquet mode? I mean, it just says to pull and it becomes a tourniquet, so, since it's a pure constriction deal, and it's likely designed to not come off easily, which is part of what they want, making me think this might be slightly problematic for them.
For law enforcement, I could see SWAT teams getting them, definitely, but regular police officers might not be the fastest to pick them up. Expense alone would likely dictate that the average cop on the corner (sitting in his temperature controlled car, of course) won't be seeing these any time soon.