Basically, H&R are more sporty than Eibach's which have a more oem ride. I wanted to firm up my cars adaptive ride in comfort for road and then have sport / sport + for occasional road and/or trackdays. Had eibachs on my 3 series with matched bilstein dampers - v good but wanted a firmer ride, hence why I opted for H&R springs.
Comfort now feels like default non-adaptive ride and sport is firmer still but useable on the road.
Lots of details in the attached thread.
http://www.babybmw.net/viewtopic.php...56806&start=45
H&R parts for M135i
Sports springs -
http://web1.carparts-cat.com/default...E107004&12=130
ARB's/sway bars -
http://web1.carparts-cat.com/default...E107004&12=130