Turn by turn navigation almost unusable

The position is slightly lagging but that's just about normal with GPS navigation. Note that even for calculating speed, there's 3-6 second delay on literary every GPS head unit out there. 

As for turn-by-turn, I really would not want to rely on it inside a city. Not that I ever tried. With so many consecutive turns, it may actually be confusing. There can also be intersections with two or even three directions which go "right" from the perspective of the cyclist. 
In my eyes, turn-by-turn is for navigating long stretches of road with few turns. Off road and inside a city, I want to see the map to get a clear idea of what's ahead. 

If roundabouts aren't showing up properly then there is an issue with the map.  I had a similar experience with my 830 - some roundabouts were not shown as roundabouts in the TBT notifications..  I stopped using the Garmin map and used one from a different source and roundabouts were correctly notified.

When TBT notifications appear you are shown the map screen, if you are not currently on it, so you should hopefully be able to see if there is a turn shortly after the one you are approaching and you don't have to fully rely on the text.

What Wongataa said - some (not all!) OSM maps will work better. 

However, the result will be mediocre at best, it is still laggy and you get extra TBT prompts to exit the roundabout... minor issues compared to Garmin map. 

There is an open support ticket for this - the more people complain, the quicker it will be fixed. 

Thx, meanwhile found you post in the 830 forum. On the full map screen, everything works fine - I see the roundabout and where I have to exit it and also see the navigation arrow for left/right and right/left turns. If the map view for TBT navigation would show the same, it would be fine.

Will also try an OSM map and open a ticket.

yeah, turn-by-turn navigation inside a city could be a real challenge for the unit. But when I go road cycling to experience new routes oustide any city, there will be roundabouts (we have many here in Germany) and quite often two turns within a 25m range.

Interestingly the map screen does it all well. I used that on Sunday for a new route created on Komoot and it worked very well. But I would prefer to have the data screen on, with my most important parameters and only get navigational hints for turns.

Early days still for me.....haven't done a real ride but playing with it in the car I can see the benefits of the faster CPU..... My position locator the blue dot can b seen moving along the white navigation arrow. Tat did not happen with the 520 plus which was a real dog of a GPS. You would wonder where exactly u are when the navigation white arrow appears. The CPU cannot display the blue dot with white arrow together.