Basically it comes down to how much you'd like to spend for comfort and convenience. Navigation on phone works alright, but it'd be a hassle to use (fingers, screen, security/water resistance) and it'd be a bigger hassle to keep it charged in a long ride. Bright, colorful and hi-res phone screens drain the most battery, then cellular (if reception is low it'll drain more than usual) and then GPS. A head unit only has GPS and an adequate non-drainy screen with better visibility/interaction. (considering your ANT+/bluetooth usage is similar in both products)