I am a regular user of the Maps app on the iPhone. I travel in the car a fair amount for work, and I routinely use it for navigation to new and less familiar locations. I will also use it even for trips to familiar locations because I like that it provides the projected arrival time, so I can tell if I'm on-time. If maps would actually also indicate my current speed it would be just about perfect. In short, I've got Maps up and running a lot of the time.
On my phone I use a protective case by Rokform that works with their mounting system, and I pair that up with the car mount that they sell. With this combination in place with a plus-sized iPhone you have a pretty decent in-car navigation system. The only downside is that, for longer trips, keeping the screen lit and the GPS running the entire time can drain down the battery somewhat, even with it plugged in to power.
I recently discovered a feature that, I will admit, may well have been present for some time, but it was new to me: If you lock the phone while navigation is running, the lock screen will light up with the maps app each time a navigation change is in the offing.
This means that the screen is dark for much of the trip, and so not using nearly as much of your battery charge, but that it will light up for you when you are, say a half-mile from the next turn, exit, etc, that you need to be aware of.
I noticed this because I was in a situation where I needed navigation, but my battery was rather low. My destination was one where I was familiar with the first two-thirds or so of the trip, but I was going to need help finding my way through the last portion of it. So I started navigation at the beginning of the trip (didn't want to have to try and enter a destination in while I was on the road) and shut off the screen, figuring I would light it up when I needed it. Pretty quickly into the drive I realized it was lighting up to provide directions, staying lit until I got through the change, and then going dark again until the next time.
I've since tried this for multiple familiar trips just to be sure it was happening reliably. It seems to be, and appears to work well. In some ways it can be a little more useful than simply leaving the navigation up on the screen for the entire trip. Under those circumstances the map is just something you glance at periodically. But with the lock screen on, it changes sufficiently to draw your attention (from blank to lit), ensuring you are consulting it when a change in direction is required.