Some of the newer Garmin Edge models will only accept FIT files. The recent 20 & 25 won't take GPX or TCX (I don't know about the just announced 820/820 Eplore, but will try to find out). I don't know if that is an increasing trend that will cascade through newer models as they replace older ones or whether it is just a "feature" of the more basic new models.
Being able to split a route into 2 (or more) sections would be useful. It could then be possible to plan a whole multi day trip in one go and then decide where to split it afterwards.
I don't know where the problem is but there seems to be an oddity with the mapping of Hare Lane, East of Chester.
A section of it is displaced north west by over a mile on the map (http://cycle.travel/map/journey/21424). As far as I know it is still in the normal place (& open for travel) & seems to be correctly rendered on openstreetmap.org.