I have Koni Sports with 2011 M Sport Springs on my car and I love the set up. I suspect that Koni FSD's would provide a similar benefit in handling, although without the adjustability of the Koni Sports.
My car is a 2009 135i that came with M Sport springs. For 2011 BMW changed the springs (at least the rear ones) from progressive to linear. So I picked up a set of 2011 springs and swapped them for my 2009s and at the same time replaced my stock dampers with Koni Sport dampers. My car also has an M3 (E93) front sway bar, M3 control arms and tension rods and Alufelgen SF-71 wheels with Hankook Ventus V12 Evo tires.
If it were me I'd go with the Koni Sports over the FSDs just so I could dial in the ride and performance I like. But if you don't want to mess with adjusting the dampers the FSDs would still be an improvement over the stock dampers. They are one of the weak links in the suspension anyway.
2009 BMW LeMans Blue 135i/Dinan Stage 2 tune/Alufelgen SF-71s/M3 suspension components/Koni Sport adjustable dampers/ETS FMIC/M3 paddle shifters/Alpina B3 TCU flash