I had a Montana and returned it as it developed a problem. I had to return the replacement unit for a different failure. I didn't go for a third. Obviously other people will have different experiences. Even so, buttons have advantages over touchscreen in inclement weather. And you already have a touchscreen device.
Garmin have just released a GPSMAP 66 and it's seen as a reasonable improvement on the previous models so the previous ones (62, 64) should start to cycle through EBay. They're button based (so you can use in the driving rain, thick gloves, etc.). (There's a 62 on there for a buy-now price of £135).
As for you phone,
get a second app. Redundancy is a lifesaver! (Just as you should always have a map with you even if you have both a phone and a GPS). If Viewranger fails then switch to another using it's own already downloaded maps. I'm having great success with Oruxmaps so far, it's stupidly feature-rich for £3 and it snagged OSM for free in a heartbeat, and you can upload other maps to it too.
A note about Garmin's Basecamp -
anyone can use it. No Garmin device required. It's a free download, and you can get easy-to-install Open Street Maps ready for it for free.
https://www.garmin.com/en-GB/shop/downloads/basecamphttps://shop.talkytoaster.me.uk/product-category/free/There are other places you can get maps from too, but those maps are free & quick to install.
I use Basecamp as my "hub", downloading routes from Walk Highlands, making my own routes, downloading routes to Oruxmaps, or creating them in Oruxmaps and uploading them to Basecamp.