A more nuanced view of this by DC RainmakerGarmin are very poor. Wahoo are the best cycle computers by far.
What I have found on the Edge Touring is:
* If you use a tcx file you will get the upcoming elevation shown (so you can see the hills to come). You don't get that with a gpx file.
* If you're doing over 100k it's probably best to slice the route into chunks and navigate shorter bits.
* Sometimes it will accept a route and navigate it OK if you set it up before you start, but will refuse it and give error messages if you ask it to start navigating when you're part way through the ride.
* My experience is: Once it works, it works fine, but getting it to accept the route and start navigating is the hurdle.