My Bikely has downloadable routes but if you go down that route I would recommend that you replot the route yourself (on bikehike for example) as you will then be sure to have a complete route that works.
I never use other people's gpx files
I use bikeroutetoaster, where you can save
all your routes, including 'starter blocks', for example I have one that goes over the Severn Bridge to the first rbt at Chepstow, and I load that as the first step in any route to Wales that I am planning. Similar across Bristol or past Bath on the C/Ps. If you were doing these from scratch they would require some manual messing around cos the Cycle Paths are not used by the route planning websites, so adopting a "here's one I made earlier" appraoch, a la Blue Peter, makes sense...
On bike hike, if I download the route using the first .gpx option, (gpx route) my Garmin won't use it, giving me a message that says something about only 100 points.... Should I use 'gpx track? What's the difference?
Bikehike is very useful to reverse entire routes, but you still have to go in and correct one way sections, especially when there are dual carriageway sections and large roundabouts..
When using other people's gpx files, which on some rides is the only way, I tend to load them into bikeroutetoaster, and then check for oddities (way off road behind the hedge pee break expeditions, for example), and cut them out, then redownload, and then the file is in the format, the 200 metre warning mode and the number of way points etc that I always use, and that helps...