I was researching the 595LM to replace my NAV 5, and couldn't find any decent interface walk through videos on youtube. I made something quick in case it benefits others. I ended up returning it soon after. The Nav 5/6 both feel archaic, while the 595LM is a bit more modern yet still old world. I understand the need for a dedicated GPS device for some, i'm not going to argue that. For me though, I ended up choosing a jailbroken iPhone as my main device. I have it set up so I can run two apps side by side. EDIT: I started using Galileo as my full time NAV replacement.
Garmin used to make a dedicated GPS device based on the Montana, called the Monterra, that actually ran android. This would be ideal for me as it would have the benefits of having a dedicated GPS unit, but also with the ability to run other apps at the same time. Sadly, they dropped support for it, and never updated the core Android OS on it.
Here's the video walk through. Real simple video.