I see one everyday cuz its on my car. It was installed on the car when I bought it off the lot - which I did not purchase because of the spoiler
I think its OK - car looks good either way. The BMW spoiler certainly is not flamboyent but adds a bit of finish to the rear end and does not seem out of place with the look of my TiAG sport package. I've seen spoilers - even from hi-end tuners - that say "aftermarket" - and the BMW version does not, imo, fall in that category.