For years now, some of our biggest FOH engineer clients (running sound for Tom Petty & The Heartbreakers, Black Sabbath, Paramore, My Morning Jacket, and more) have known that putting a REFLEXION FILTERr in front of their amp cabinets can help reduce stage bleed into their guitar mics. This is especially true with some of our favorite guitar mics like the VR1 and RNR1 ribbons, since they naturally have a figure-8 pattern that leaves them open to whatever else is happening on stage.
This doesn't just help the FOH mix either. Using an RF on a guitar cab or drums can make the multitrack of a live show significantly easier to mix.