I purchased the Lexus air filter because it was supposed to be a "carbon air filter" but I did not notice a difference in a certain area I drive in that smells like horse crap. But in the Benz I don't smell a thing in that same area.
Indash for me
I personally like the indash system. I have an older model that also plays dvds.
http://www.pioneerelectronics.com/pna/mec/category/two/0,,2076_3149,00.html