Dedicated bike GPS computer over smartphone
I used a phone for about two months, then bought a Wahoo GPS computer in March 2018.
The primary motivation was that


My phone has lousy GPS (Huawei P10).  Multiple times a week, it would claim that I'd teleported half way across town, lose signal and never get it back, or drift so that the track would look continuous but end up hundreds of meters from my destination.  I hear that iPhones have pretty good GPS.  My Wahoo has near-perfect GPS; the worst it does is beep at me in forests on cloudy days because it thinks I've wandered too far off the side of the road.  Some speed sensors can talk to phones by Bluetooth, which may improve phone (and cycle computer) tracking accuracy.


Other advantages:


Size and mounting. My phone isn't big, but it's much bigger than my Wahoo and I found it somewhat inconvenient on my handlebars.
Battery life.  My Wahoo claims 15hrs. I probably get more like twelve, but that means I only need to recharge it about once a week.  Six hours of battery life would mean that, if I set out on a 4.5hr ride without having my phone fully charged and things took longer than I was expecting, I could easily be caught an hour away from home with no GPS and no way to call for help.  Which is to say...
Redundancy. Having a cycle computer and a phone means that I have one device to keep me safely on the right track and a separate device that will give me backup navigation and, in the worst case get me help.
User interface.  The Wahoo has six buttons. While I'm riding, I can press the buttons to get to the screen I want without looking, and then glance at the computer to find out what I need to know. Touch-screen navigation of the phone requires you to look at it and is awkward when things are bumping around. I put the phone inside a waterproof pouch (because, England) but found that made the touch screen awkward to use.  Touch screens are a pain with gloves, too.
Crash resistance.  The one time I've crashed, my Wahoo (and my knees and shoulder) got scuffed up against the concrete in a way that I'm pretty sure would have wrecked my phone, but which caused only cosmetic damage to the Wahoo.  My phone was in my jersey pocket and was completely undamaged and available for use if I'd needed to take photographs or call an ambulance, or a friend or taxi to get me home. Of course, one can easily imagine  a crash in which the contents of one's jersey pocket get trashed, while stuff mounted on the handlebars survives. On the other hand, the phone felt much less secure on the handlebar than the Wahoo does.


In other words, not much has actually changed.  The only thing I've not mentioned that came up a lot in the previous thread was screen brightness.  I guess my phone's screen brightness would probably be fine, but it was kind of moot, as I never did figure out how to stop it blanking the screen after a few minutes of riding.  I'm not sure how my phone would have coped with being in its waterproof pouch on a really hot day; I only used it in the English winter.