In the words of Boss:

Building on the 20-year legacy of the famous BOSS BF-2, the new BF-3 flanger pedal gives guitarists and bassists an updated version of the classic BOSS flanger with the thickest stereo flanging sounds ever. Two new modes (Ultra and Gate/Pan) create stereo flanging with incredible depth–even Slicer-type effects and sounds that seem to “swirl” around the listener. An instant classic.