Great answer, even with a proper technique, I quess you would still get some sting from the alum, correct?Yeah, Its a good indicator on where your technique slacked a bit and cut too close to skin or put pressure on blade. The reason the stinging is most obvious under jaw line is because, as you say, these are the hard to shave areas and there is more chance of slipping up when shaving there, myself included. Alum is great for sterilizing skin post shave and closing pores to prevent irritation and helps reduce razor burn significantly. You will also be sure to pay closer attention to shaving technique knowing that you will be using the alum afterwards, OUCH, haha!
Will you still fell a little sting even with proper technique?