Questions Prior To Getting Edge 1040 (Non Solar)

It will switch to a zoomed-in map page with the turn shown with an arrow a hundred metres or so before you get there. You don't say if you have prior experience with Garmin Edge devices - I'm guessing not - but the behaviour is basically unchanged. 
You should be aware that the unit's decision on whether a junction is ahead can be a bit odd. It's largely based on the geometry of the junction - if it thinks you need to actually "turn" it will tend to display the instructions, if not, it does nothing. This can be annoying - it gives instructions when the road veers left, but "ahead" is someone's drive (so it's pretty obvious), but fails to warn when the road you're on veers left at a junction, you need to turn "right" but "right" means more-or-less ahead; it will then just assume that you know. You need to be aware of the latter, because if you're relying on instructions being fed to you, they won't be, in all cases. I guess it probably happens every 30 to 50km, but obviously it depends on the nature of the roads being used. 

If you go off course, it will give you an option of pausing navigation or recalculating. If you select neither, it seems to do the latter. I've found that its effectiveness in such situations is variable - sometimes it makes ridiculous suggestions (not often, but it once asked me to ride a kilometre or so, do a "U" turn, and retrace the way I'd come, when the best route was dead ahead - half the distance on the same sort of road), sometimes it takes so long to recalculate (thirty seconds??) that you're back on the planned course before it's done it, and usually it's good. 

Thank You, I have an edge 800 but that does not seem to have a pop up that warns me I have a "Turn" coming up (I tested it this morning specifically for that facility, I was following a course I had made up in Garmin Connect but viewing the virtual training partner screen - And that just let me go off course without any advanced warning of Turns) The redirection back on to a course sounds a good feature, sure I will get plenty of use from that bit

Amazing how quickly one forgets what things used to be like - I skipped the 800 and went straight from a 705 to a 1000, and I'd fogotten how turn-by-turn was once not taken for granted!

You might be interested in this thread - I think turn-by-turn was an option for the 800, depending on the way the course was created and the maps being used - forum.bikeradar.com/.../turn-by-turn-directions-on-garmin-800-gpx

Ha, ha! Well, if it makes a difference, I think you'd notice the difference with the 1040. The 800 had a really good reputation, but the functionality of the 1040 is pretty amazing. I missed the 1030/1030 Plus and switched straight from a 1000, and even for me the metrics measured and recorded are staggering! (You need to be a bit of a metrics nerd to appreciate that though, probably. some may just find them annoying!) 

Indeed, there are plenty of tags being collected and computed in the 1040 head unit. As a civil engineer involved in automation, SCADA, I am also a data junkie.