Decent. Traffic very very useful. Good when it works!

UPDATE 1/22/16: This app is good when it works but usually after several times of use, it fails to automatically reconnect to the GPS and you have to turn Bluetooth services off on your nüvi and then turn them back on which is extremely frustrating. Occasionally, you even have to repair it with the phone and this is happened on multiple iPhones Ive used. Also, the map quality on the app itself is atrocious. It only shows major routes and you have to zoom way into even see anything. They need to update the resolution map quality to be more in line with Google maps or Apple Maps.

UPDATE 9/16/15: A mess after iOS 9! Garmin has not updated the app and now its horrible. Blank white tabs that are unreadable. Also crashing on voice entry when searching. Please fix asap!! Garmin says a fix is in works but may be too little too late.

Needs work but traffic is the most valuable feature and provides better coverage than the FM traffic receiver on the unit

Iphonerocks00 about Garmin Smartphone Link