Definitely mount it where the helmsman can see it. If possible, mount it where he/she can reach it to push buttons. No question here.

Now, about the Lowrance broadband. First, let me say that my experience may not be typical. I haven't been able to confirm it with other users.

The close in performance of the Lowrance broadband is head and shoulders above the Raymarine RL-70 units I had on my last two boats. No comparison here at all. However, beyond 100 yards, the performance sucked big time. Tall, steep volcanic islands only start to show up at 4-6 miles away regardless of how you fiddle with the settings. Freighters can be detected at no more than 3-4 miles. On my last cruise to the S. Pacific with the newly installed Lowrance broadband, I was very disappointed in it's performance. On my list of things to do before our next cruise is to either find out what the problem in my setup is or replace it.

FYI, it's mounted on a tower at the stern. One of my other boats had the RL-70 at the spreaders and the other had it on a tower. If there was a difference ion the performance between the two, I never noticed it.