I run the 595c and have been very happy with it. It is a very easy to use unit which I really like. All you have to do is turn it on and go 
I am also running a Navionics Premium North chip with it and has worked flawlessly on the river and the few lakes I have been on.
I have never lost GPS signals, ever.
The screen is plenty big, setting the unit up is very easy, and the different screen views are nice and easy to change when needed.
For the price, you can’t go wrong, IMO 