Thanks, FF, that's useful. In fact, I did try it in Prompted mode, but it seemed no different to Off-Road. Maybe I didn't try it long enough though.
I'm sorry, I didn't explain it very well. 'Prompted' isn't a routing mode as such, it just means that every time you select a Route you are asked to choose between 'follow road' and 'off road'. Without this, if routing is set up to be always 'follow road' for example - which is how a lot of people do set it up - you essentially have a GPS that is broken when any Route with >50 points is loaded.
As for a warning, when you download a GPS file from cycle.travel it does give you four options: "GPX track (works on all devices), TCX course (best for new Garmins), GPX route (small file), KML (Google Earth)" and I now know that "small file" means "only use this for small files" rather than "this is a small file"! Also, tcx files might be best for some new Garmins but they don't seem to do anything at all on mine!
No, Etrexes can't handle tcx files.
I don't know the particular planner you've been mentioning, but quite simply most online planners seem to have this in common: - that they happily and without warning produce
broken Route files that
no GPS can handle. What they all seem to do, if you select Route as a download option, is to give you a Track file that has been crudely converted to 'Route' simply by altering the code such that every point is tagged 'Routepoint' rather than 'Trackpoint'. This simply isn't good enough, because a Track may have thousands of points and still be usable, whereas no (Garmin) GPS can handle a Route of more than 250 points. Just converting one to the other so crudely, without regard to these differing requirements, is dismal.
The popular BikeHike planner is a particularly bad example of this - if you just use it in what seems like the most intuitive way, you will end up with a broken file. Despite that, if you use it in ways that aren't 100% intuitive, it's an excellent planning tool that can produce files (either Track or Route) that work well with the Etrex20. RideWithGps is another very popular planner that will offer up broken files in exactly the same way.
(You were lucky, that your Route was so short that it didn't actually pass the 250-point limit, so wasn't a complete disaster. If it had been longer, the first you'd have known about it was when the purple line just stopped in the middle of nowhere. Many AUK organisers still offer GPS files for their events that do exactly this.
)
I used 'off road' routing for some time but only ever got audio alerts at waypoints, never turn instructions.
Well yes - if you want nice verbose instructions on an Etrex, then you do either have to use 'follow road' or put a lot of work into hand-crafting your own direct Routes. Ironically, if you do rely on 'follow road', it works best to place points NOT at junctions - but instead partway along roads in between junctions. The reason for this is that the 'approaching waypoint' instruction will interfere with the more useful generated turn instruction, if you put a point too near the turn.
I use 'follow road' if I'm happy with 'quick and dirty' - which sometimes I am, sometimes not.