I have nothing but positive things to say about my Edge 510. OK it doesn't have mapping, but the "breadcrumb trail" navigation is pretty reliable. The unit has more features than I'm ever likely to make full use of. One real positive is that it uses both the American GPS and Russian GLONASS systems, so positioning is supremely accurate and reliable, even when under cover of forests or built up areas. You can also switch GLONASS off to give longer battery life.
Personally, I would always prefer to use a specific bike GPS rather than my phone, as I used to have reliability issues with Strava dropping out, and the way most smartphones suck up battery power, you can just bet your phone will die on you when you're miles from home and need to call someone to pick you up because you've wrapped your rear mech up!