Butter oil is, in my understanding, the fats from butter after everything else has been removed. In that sense it’s not unlike clarified butter, but probably made with a centrifuge rather than heat. Adding milk powder (and presumably some water) sounds like basically adding back in what got removed to make the butter oil. I would hazard a guess that this is done because both butter oil and milk powder separately have far longer shelf lives than butter does

So I think that it’s basically the same components as regular butter, they’ve just been separated out and then recombined. I have no idea if this does anything to the flavour