This is a vintage Musitronics Mu-Tron Flanger electric guitar effects pedal. This particular example, serial number 1395, is in excellent condition and includes a (non-original) form-fitted box! This extremely rare pedal is considered Mu-Tron’s best.
According to Mike Beigel, Musitronics co-founder and pedal designer, only 1000 Flangers were produced, which is what renders this pedal so scarce today. While the term “flanger” typically prompts a negative connotation with most musicians, it is this particular flanger that will absolutely dispel any such misgivings. This flanger is much more than a psychedelic sound effect, as this pedal somehow creates an incredible plethora of exciting textures, truly unlike any other pedal I’ve ever heard. Unique in every way, this dynamic effect is super musical. You can sit and listen to its sound waves for hours, just as one could watch the ocean, without it becoming predictable or uninteresting.