Indeed it's quite an unusual piece
It's actually a re-purposed BF-2B case (a Japanese one no less

).
Inside is a completely different circuit board (professional green PCB) covering the entire space much like a BOSS one.
Circuit wise it melds a massive 4 x "EP Booster" circuits (Echoplex preamp), in a stereo configuration. There is no bypass, the effect is always on, with the FET switch replaced by a standard stompbox switch inside. Operation is surprisingly smooth.
In practice you can essentially run two amps with two clean and two boost levels, L & R, Green/Red channels. Quite useful if you are a fan of the circuit, and you can boost different amps by different amounts pre-set.
Very well made and a unique item on the BOSS shelf
I haven't had much of a chance to put it through a good test, though may do so soon.