Is it save? Yes. Though you'll find that some enthusiasts swear by them and others will tell you to stay away. I use them on two Benzes and I use the stock MB airfilter on the third.
I can tell you in actual fact that after polishing the manifolds and cylinder head on my 190SL the stock airfilter starved the engine for air. It actually ran out of air at about 3900 rpms. I use K&Ns on my 190 SL and my 190 E 2.3-16 (10.5:1 compression). I use the stock filter on non-modified my 300 D. What I'm saying is I doubt there is a need to switch airfilters unless you have modified the engine and have increased your airflow.