Like Mellow, I have a Garmin 590LM. If interested, there's someone in Holland that provides firmware to load onto a 590LM and make it a 595LM.
I thought of using my Samsung Galaxy Note 4 as a GPS. The idea of having my $6-700 smartphone possibly come off a holder and bounce on the road turned me off on the idea. The tether on the RAM Mount took a long time to get it attached. Then it seemed like on full brightness, in the hot summer sun, it would overheat. A couple car GPS's didn't work well because they didn't have Bluetooth and the screens washed out in the sunlight.
I looked seriously at the TomTom Rider at the time. It's a great GPS, and the Winding Roads feature works far better than Garmin's equivalent...or at least in this area. My biggest objection was the screen size. With the Garmin 590/595, I got a 5 inch screen. With the TomTom, it is 4.3 inches. Some of that is recovered by TomTom with a thinner information strip on the right. If I was looking for a new GPS, I'd look very closely at the new models.
Many people look at a GPS as only for navigation. It can also be used to get a look at the road ahead. In the picture below, you can see that the first turn is pretty easy, but the one just after that will require slowing down a lot.
The perspective on the screen is important. I've seen some give you a good look ahead at the road, and others that were worthless.
Chris