Kevin,
  My understanding is that Chelton computes AOA rather than actually
measure the lift the wing is creating, using inputs provided by the
operator.  If that's incorrect, I hope one of the Chelton gurus will correct
me.  The AOA Pro or Sport measure actual lift by comparing pressure on the
top and bottom of the wing.  Based upon that, my impression is that they're
more accurate.
  Sip Slater