, turn guidance on, you get an audible beep and a little text box popping up to tell you to turn left, or right, etc.You get the beep and text box without "Turn Guidance" being turned on. They come from the course points. "Turn Guidance" and "Course points" are two different things. "Turn Guidance" doesn't work. It generates the purple line that doesn't follow the course. If it worked it would generate turn prompts different than the course point prompts.
I haven't tried using turn guidance but others have said it doesn't work. I recommend turning it off and using course points.
If you are not familiar with course points, they can be added by route planning software to tcx files. They contain a location and turn direction. When you reach the location there is a display at the bottom of the screen that shows a small icon for the turn direction. You can add a data field, "Course pt distance", that shows the distance to the next point along with the direction icon. I find that field very useful.
I use RidewithGPS and with a slight modification to the file have no problems. Just plan a route with it and output as a tcx file. The points in the cue sheet will be added as course points. Use a text editor to modify the "TotalTimeSeconds" entry towards the top of the file. It is way too low and needs to match the total times between the first and last timestamps. It has been noted that you can just add a zero to the value. That modification is needed in order for the 520 to find the course if you do not start at the beginning.
Unless you have premium membership, RidewithGPS puts the course points right at the turn. It is better for them to be before the turn. BikeRouteToaster and maybe GPSies will put them before the turn for free. There are some other treads on this topic