A dedicated GPS is an invaluable tool for dual sport riding. Since backcountry routes are often far from cellular service, using a cell phone mapping app may not be possible if it relies on network access for map data. There are apparently ways to use some mapping apps offline (like Google Maps), but I don't have much experience with this mode of operation and have found it unreliable. If you need to download data for your route ahead of time, you may end up being stuck if your route needs to deviate outside your planning zone. Of course, when plans fail in the boonies, true adventure can be the consolation prize.
Garmin makes a bewildering array of GPSes for different applications, often with overlapping features that can make it hard to choose the right model. For the past 15 years I've relied on models in the handheld series, including the eTrex, GPSMAP 60csx, and GPSMAP 64st which is the newer version of the 60. Unfortunately, two years ago my otherwise trusty 60 began suffering intermittent power failures, which motivated me to upgrade to the 64. Unfortunately, my brand new unit had a button fail after a couple days of use. The warranty replacement suffered from a flaky power problem a year later, finally bricking the device and losing all my data from my 2017 RAP trip. The next warranty replacement unit, which I just received about a month ago, has started showing intermittent power problems as well. Apparently I have a knack for making electrical things fail. Either that, or I need to check my USB charging port on my bike, which otherwise works fine with my iPhone.
Despite these reliability issues, I bit the bullet and sent Garmin even more money, this time to upgrade to the Montana 610 purchased from GPSCity. The 610 is significantly bigger than the 64, but my aging eyes immediately appreciated the improved readability of the larger screen.
The 610 is also a beefier unit overall, and incorporates a power connection method that is ideal for mounting on a motorbike or ATV using a RAM system. While the old 60 I started with used a rugged four-pin connector for power and data, the 64 replaced that with a micro-USB port. This is fine for charging indoors, but is simply not durable enough for exposed use on a bike. The Montana mount is a vastly superior design and it's really not worth considering anything less.
Since there's lots of info online about the Montana 610's specs, I'm not going to repeat them here. I will say that the touch screen works very well with gloves on and overall the unit is far more usable (and therefore safer) than the 64. Setup and pages are essentially the same on both units, so if you're familiar with one, it only takes a few minutes to get used to the other. And of course, Garmin's free Basecamp software makes it relatively easy to create routes and manage data on and off the device.
If there's an obvious beef with the Montana, it's the crappy basemap that comes with the unit. Yeah, you can fork out a couple hundred bucks for a better map, but already this is an expensive device and my Nuvi 2455 (also a Garmin), which cost $100 at Canadian Tire, came with lifetime map updates (and they're frequent, too!). I don't mind paying for quality maps, but not over and over again--especially for topo maps, where updates generally occur on a geological timescale.
I installed the Canada Topo 4 map on the Montana and added the Backroads Map for Eastern Ontario on SD card, but I was initially confused by why the topo map didn't appear. Then I remembered that while Garmin allows you to activate multiple map sets on the device, it only displays details of the topmost layer. Details of any other maps are obscured. The only hint they're actually there is the occasional blip you see when the screen redraws a layer and then the next layer over it. To avoid this problem, you should only activate the one map layer you actually want to see.
Installation on my bike was fairly straightforward using the Garmin power mount. Don't forget to order the RAM plate for the rear so you can attach the mount to any standard RAM arm. I decided to wire the unit directly to the battery rather than through a switched circuit like for my last GPSes. I've found it a nuisance to have to constantly ensure the device remains on when switching off the bike, e.g. when stopped to check something on a trail or refueling. There's now an increased risk of the unit draining my motorcycle battery, but this should be minimal in daily riding when the Montana's internal battery is already charged. For longer off-periods, I'll need to remember to remove the device from the cradle.
Overall, I'd say the Montana 610 is an improvement over the 64. The cradle and power system are robust and designed for motorcycle or ATV mounting. The touchscreen is highly usable with gloves on, and the features are comprehensive and easily customizable to different scenarios and preferences. Cons are price and poor basemap. The Montana 610 is essentially unusable unless you buy some sort of optional map for your riding area. Also, the UI is sorely outdated, slow, and somewhat clunky compared to mobile phone UIs from even 10 years ago, but it does work.