Used it on my German trip. All was good, no technical problems.
A couple of routes I planned worked 99 percent OK
One issue is that when you don't zoom in enough in basecamp and you place the marker slightly off the road, up a side street, the Zumo won't forget it. You ride past and keep on the route but it is constantly trying to turn you back. The old 550 used to forget pretty quickly and carry on but the 590 won't. So I was holding the others and shooting up the side road to the point and coming back :lol I eventually discovered that going to mini settings screen from the map you can tell it to ignore next point - phew!
The round trip app worked quiet well when nav is set to curvy routes. It does take in a lot of minor roads but hey, you get to see some of the countryside you wouldn't normally!
One niggle is that you have to go into the main nav settings to change between fastest or curvy route. When you need petrol and add it as a via-point it does it curvy and not direct!
So when you want to come home and tell it to take you 400 miles to Calais and it's still on curvy routes it takes 10 minutes and then gives up. Took me a little while to work that one out I can tell you. Once set to fastest route it took all of 10 seconds to start navigating.
Sometimes Doris was a little late in announcing Turn Left here.