So the question is really "are some OTC washer fluids potentially damaging to [plastic] headlights?" I don't know the answer to that for sure, but I have to assume not since the majority of headlights these days are plastic...although not so many cars have headlight washers.
I personally, years ago, had a washer pump fail in a GM car shortly after putting some cheapo washer fluid in (can't say whether this was really the cause), so I used to go to the GM dealer and get Optikleen (the GM brand). I don't recall it being very expensive, really, but none of the dealers seem to have it anymore. Perhaps the BMW fluid is reasonably priced, and you can stock up next time you are there.