total and complete bullshit. the box probably doesn't even have circuity in it.

there's no known way to externally control fueling (or timing or anything else) with OBD-II comms in a universal and generic way that would apply to 'any petrol or diesel powered car'. reprogramming fuel tables or dynamic control of fueling just isn't a universal thing.

if such a thing did work, the technology would be way to valuable to put into a $50 box.