To begin with they were JUNK!!!!!!!!!!!!! I bought a LMS-334C and it would not hold signal.
MY unit was mounted behind a winshield, this was the problem my dealer said.
I sent the unit in, and the factory installed new software. It is much better now, but far from perfect.
I am happy to say that the new units are said to have a larger antenna in them. This should make them a great unit.
Your call. Over all I love my Lowrance