I have the sea hunter II and use it mostly in fresh water, it goes deep, pulse induction. I like the ability to tune out pull tabs, but... And I'm speaking from experience not necessarily fact, you will find a particular area where the targets are all running the same approximate depth. Tuning out trash in that area helps, but if there is a good target deeper you will loose it. This is where I think the VLF machines are better, variable tones, and better disc. PI machines are limited in discrimination, and no tone separation.
I have only tried to hunt in the Atlantic ocean when it comes to salt water. It's tough, waves move you around to much at waist deep and lift you up at chest deep, about the best I could manage was knee deep. The gulf coast may be easier. If you were diving then sea hunter goes 200 ft deep so probably a winner there. But shore hunting...good luck, I just stay in lakes rivers and streams. My advice be there at low tide, hunt on dry land with a VLF.