Couldn't pick a worse round for an Air Marshall to carry. Overpenetration should be a concern when firing a gun on a crowded airplane, which makes the .357sig a bad choice. Also, airplanes are relatively confined spaces. Tapping off a high pressure .357sig in a confined space will almost certainly cause severe hearing loss/impairment compared to say a .45acp or a 9mm. Just a bad choice all around.
Right. They have no idea what they're doing.
I think they have a tiny little bit more expertise than the average joe.
New Mexico State Police also use the round in addition to the agencies already mentioned.