WRT battery life, I barely get a day out of my iPhone using it for guidance when hiking. Based on that, I suspect it would just make a 200k. Battery life on a nav device is important to me, the new 1040 with solar giving 40+ hours is tempting.
The best field on the Garmin is "Distance to Next"......I almost never miss a turn with that function. I doubt a phone based bike nav would have that functionality.