COBB Tuning provides a flex fuel sensor for my car, for 700 bucks. COBB also provides my engine management that allows me to run aftermarket / pro tune engine maps. Tunes are done on a dyno. The flex fuel sensor works in combination with my accessport(engine management), along with fuel pressure and ethanol % gauges that will adjust boost and timing accordingly depending on how much ethanol the sensor detects.

Pros:
Lower chance off detonation.
Run higher boost and timing.
Colder charge (hence less det)

Cons:
HORRIBLE gas mileage
Must get rid of immediately, cant not let it sit in your car. Will corrode parts.
Hard to get E85* fuel. Not readily available depending on location


*Not always E85. Concentration levels change on season and gas station