My wife has actually been using the in vehicle navigation on her Suburban more so in/around town than her smart phone. On our Suburban, while not as quick to update for traffic, it has rerouted us due to traffic congestion/issues. For long distance trips I do like to use something like Waze as I can look ahead for traffic issues along with being warned of objects in the road or pot holes. We actually often run the in vehicle nav and a smart phone on road trips.
We do seem to have an issue if using a smart phone for navigation and listening to the radio after giving instructions the radio will not come back on. If we are streaming music this isn’t an issue and it isn’t an issue with the in vehicle nav. Other than the vehicle nav becomes a nuisance to the young kids when it talks over their movies!
A few things I do like about having OnStar...the other day I met up with the wife and she was then heading to a different location than I was, somewhere she hadn’t been before (we have only lived in our area nine months). I looked the place up on my phone and hit the send to vehicle button. Within seconds her truck nav was providing directions. I also really like the remote access features through the app. It’s nice to be able to come out to a heated or cooled vehicle when you have an infant with you. We have also had an instance where we were behind a drunk driver late at night but had no cell service. Our OnStar still worked to be able to notify the authorities.