I have always bought from counter assault out of Kalispell MT. Bought it because I like to support Montana Business.  Get the biggest you can buy. They make and 8 oz and a 10 oz. The holster that comes with is is easy to use/get the spray out/and or point and shoot from the hip. Never used it, but did shoot an old can once with a .45 with the wind blowing fairly strong away from me. Gotta say my sinuses/eyes sensed it even at 20yards away. I believe they expire, but that particular can started a small leak that I could hear after being mistreated for a number of years by being left in a hot car, so treat them with some care.   And also, you cant check them on your luggage if I remember correctly. Good luck.