We had a great ride in Asturias and Galicia. Wore out a set of tires!!
My issues with the navigation and roundabouts was similar to yours I think. Certainly a minority of the time. I am not certain I can come up with the exact locations but I will see what I can do. What I did notice was the number of the exit to take did not match the graphic at times. The graphic was pretty much always correct. So, like you say, it may be a matter of counting/not counting some smaller paths that may, or may not, have been considered exits. I found it more of an issue on the bike than in the car as I rely more on the audible instructions on the bike. In the car I had a good look at the graphic as I approached the roundabouts so I had a picture of where to go.
Overall, I was happy with the way the app performed.
The issues I encountered are certainly not enough for me to give up on it.