I really am glad I went with a 420. I have the non BT version. I know there are other great vendor choices that have been good to the forum members here, but I can't say enough good things about Mike's Liquid Audio if you need a authorized Wet Sounds supplier:
http://www.mikesliquidaudio.com/ . Mike gave me a ton of good advice/step-by-step instructions on how to wire mine up and avoid a noise issue that my boat is know for. Who ever you buy from, buy from an authorized dealer (not an ebay reseller) or you are screwed on warranty issues. (not that I've had one, knock on wood).
Even with a full Wet Sounds system and Rev 10's on the tower, it was a noticeable sound difference with the 420. Really livened up the audio, especially the bass, and I love the adjust-ability. I will say the mic is pretty much useless for me, my voice is too deep and I sound like Charlie Brown's teacher on the tower speakers when I try to use it.
When somebody else is driving your boat, you have to teach them not to turn down the head unit and the EQ separately. They inevitably forget they turned down the head unit, but that is with any added EQ.