I have a Riptide 55 SE hand control on my 16 ft. Jon and I use it primarily in freshwater. It has been a fantastic motor. Plenty of power and maneuverability The digital maximizer feature is a huge power saver to the point where I can fish all day on one battery. I'll need to charge it overnight for the next trip, but it's pretty remarkable that it runs as long as it does on a single charge. I don't know if they even make a 5 speed motor with more than 55 lbs. thrust. Either way, go with the maximizer and variable speed. You will need to run your depth finder on a separate battery, but you should probably do that anyway.

Here's my view on it-
- The life of the freshwater motor will be greatly compromised if it's used in saltwater.
- The saltwater motor can be used in any kind of water, so I'm assuming it is better insulated and non-ferrous parts are used.
- All ferrous metal will corrode eventually, even if it's used primarily in freshwater.

The SE motor has a compact mount and a quick disconnect is available. It uses a large poly plate on the mounting bracket and a poly puck on the boat. With the motor removed, all that remains is a 4"x6" puck. Everything else is out of the way- a huge benefit if you're duck hunting. The SM motor has a more robust mount and I don't know what the QD mount looks like on that one.

I'm rigging my boat as if it's going to be used in saltwater tomorrow. Aluminum and stainless parts are only painful to buy once. After that, you'll have something that is practically guaranteed to live longer in either environment. Plus, if you ever need to remove parts, it's nice to not have to deal with stuff being rusted together.