I'm having the Alpine KCA-420i installed this weekend mated to an Alpine CDA-9831 (although I'm thinking about upgrading to a 9835). I'll post a review once everythings installed.

 

I also have a KCA-420i sitting here next to me, and as soon as I get my new amp wiring kit, I will be installing this (hopefully this weekend?)

I hear the Alpine interface is slow ... but its recommended from several people just to make playlists... and then you only have to scroll through the playlists. I'll give a review once its done as well. I think I am gonna mount the unit under the passengers seat. The storage behind the seats will be filled with my 2 alpine amps.

 

That is why I like my setup. I have the actual iPod right at my fingertips and can use the scrollwheel to select songs. But I agree playlists are the way to go. You don't want to rear end someone cause you are goofing around with your iPod...