I have a Garmin fitness watch (Fenix 3), it has turn by turn directions, some advanced navigation stuff, and is a great bike computer. The GPS is much better than in my phone. I can swim with the watch but not the phone, same goes for running races. But the screen is much smaller than a dedicated bike computer and not as easy or convenient to look at on the bike. A watch is great if you do other sports besides cycling; a dedicated bike computer is better if you're a cyclist only.

Here's an elevation chart showing what I've done and what's ahead of me on my route - the red arrow points in the direction I need to go (you can see it's pointing ahead on the road).



And basic mapping, better for hiking than for cycling.