I have a Garmin 755t. I don't know if it's just mine or if it's a common issue with all Garmins, but it seems to take forever to find anything... like when you type a name of a store or restaurant, you're going to see the hour glass symbol forever. It won't even tell you that it was not found... sometimes it does find it, but then it takes ages to do that.
Also, th internal speaker volume could be louder. And the built-in FM transmitter is a joke - very poor reception... maybe because I have a rear-window built-in antenna, I'm not sure.
I used to have TomTom on my phone before. Granted, the screen size was a downside, but everything else seems more intuitive and better thought-out there compared to Garmin.