Thinking of getting one but havent a clue which? Hoping you Techie types can point me in the right direction. What features do they have? I currently have the factory fitted radio and use a stand alone Garmin sat nav. Would a head unit have all these features built in? How reliable are they and ease of use etc....I like the idea of having one but would like some real world advice from people who use them.....Basically...How will it make my life better...... or not!!!