I've elected not to use them due to the airflow they'd take from the cooling system for minimal gains at best. From pictures I've seen, I'm also not a fan of their design and the sharp 90 degree angles that would potentially create turbulence.
2008 AW E88--2 years on 100% E85. Too much to list..
2011 AW E90--Tune--Stage 1 Turbo--FMIC--DP
2013 Mini JCW--Tune