So, is using a third party software package the only way to merge video files from a GoPro? What's the latest gouge on how to do this best/quickest/easiest?
You can use Quik for Desktop or Mobile or even Splice if you're using iPhone.
You can also use VSDC if you're using Windows.
Frankly, after wasting several hours trying to figure this out with Quik, I gave up and I'm using Movavi. Much easier. Quik is nearly worthless in comparison.