I say keep the Zender rear...the BBS apron is fugly. The Zender unit is a much cleaner design, and I think its the best looking one for the E28. If you notice, the Zender unit has lines that start out at the front edge, mimicking the lines on the BBS spoiler...matches very nicely.
the zender is nice, and I rather much keep it. I just would like to complete my BBS body kit, as I already have the BBS front which is favorite front lip, and I also just won the BBS skirts a couple of the days a go.