It feels to me like in the canonical example, Harry generated spin on a Counterspell or Block check, and the GM allowed a bonus on a followup roll, making it a few shifts easier to cast a followup Evocation spell against the BCV.
Other options:
Spin generates a free Maneuver that places the Aspect "Redirected Spell," which the player tags to either:
A) Invoke for Effect to allow use of the opponent's element on a followup attack, if the player doesn't possess that element normally
B) Tag for a simple +2 to a followup roll to reflect the surprise factor, or the ease of recycling the magical energy - heck, the GM may even allow this to boost the Power of the spell (people ordinarily limit Aspects to helping with Control rolls).
C) Invoke for Effect (plus an extra Fate Point or two) to determine that the spell gets actually redirected to another target, no Stress or targeting roll. The GM is free to negotiate the actual cost to the player, but an IFE plus FPs should be sufficient justification.