Bob F is the man regarding these gizmos.
As Tom said you get what you paid for. The top end units has functions you probably won't need, for example, some GArmin and Raymarine can log the seabed, ie., you can go home and examine the seabed you had covered, but do you need it?
The Navman 7100 is easy to use, just pick it up and speak, while the 7200 is more expensive but with more functions. I have the 7100 and it's ok, chatted on it, it sounds good and touch wood never had to use the red distress buttom, the 5600 chartplotter is great, it shows me where I am, manual and me just don't mix, so don't ask me what are the functions.