need suggestions for 2nd humminbird unit

[tazmnaz]

I am looking for a second unit for the bow to mount to my US2 motor. All I am looking for is a good unit that will give me the definition I need to identify fish without spending extra on thing I do not need like gps, etc.
I am not even sure if I need color or can get by on mono.
I was looking at the 343C and 345C, but do not know what the difference is between these units and if I can get away with mono, then maybe the 325.
Any suggestions on what I need or if it is one of the above, what is the difference?

Thanks!