RouteScout limits have changed over time. I believe the current limits are 25 tracks, 400 miles and 12,000 points. Should be enough for most backpacking trips!
I've used it for multi-day trips in Grand Canyon, JMT/Yosemite, or just multi-day trips in the Arizona mountains with a lot of different dayhike options. I have saved multiple tracks every day of a trip. (I have an iPhone 6 ... now almost 3 years old, so not the newest, fastest, etc.)
There is no question that a phone battery doesn't last as long as a Garmin. But I'm carrying the phone anyway. And I use it for photos and other apps so I'm going to keep it charged for my backpacking trip either way. Running the GPS on it takes almost unnoticible battery compared to all my photos!
It's had some glitches from time to time, but is generally quite reliable. I haven't carried my Garmin on a hike in over two years! Largely because RouteScout pretty easy to use, and convenient because it runs on a device I already have with me anyway. Honestly, just having the topo maps on a nice color phone screen with pan, pinch and zoom makes it worth it to me.
As for the OP, I know that there are some people who love their Garmins. I hope the posts above help you out or somebody steps up and takes your money
. I don't know enough about the 64 to be of much assistance. Good luck!