Regarding Genuine vs non-Genuine parts, it's a fine balance that has to be accomplished. For certain components, such as electrical parts, I learned that it's critical to use genuine parts. For other stuff, like getting poly bushings instead of genuine BMW bushings, it doesn't matter as much.
For something like a strut bar, it simply doesn't matter which one you get. On the street, they do nothing other than help prevent strut tower mushrooming, which any decent strut brace could do. So, in my opinion, the difference is the bling factor you desire.
If you want bling, none of them even compare to the BMW Carbon Fiber brace; it is hands down the best looking brace for our cars. If, however, you like the look of a much cheaper brace, go for that one. The BMW one is too much money, if you ask me. Yeah, I bought one... Dunno what I was thinking but I'm glad I already have it!