My only "knock" against smartphones for navigation is there often seems to be a slight lag between where you actually are and where the phone puts you. In most cases, it won't be big enough to make much of a difference and/or cause you to turn early, but it seems funny given the processing power of a typical smartphone that that happens. I still think nothing beats a Garmin Edge, especially when it comes to battery life. I like that I don't have to think much about charging it and it works pretty effortlessly. Whether it's worth having a separate device for this purpose is a subjective thing, obviously.