how much are you letting that effect go for anyway bro ?
there are some physical differences other than the size. the XO BMS works on a 9V DC power supply and is daisy chainable. the BMS uses a many many volt power supply, i forgot exactly how much.
the second difference is that the XO BMS has a red LED to indicate whether the pedal is engaged. the BMS only has a power led if i'm not mistaken. any BMS owners please correct me if i'm wrong