i'm a big fan of salt away, but i'm a regular salt rider.
I'm not sure i'd say that for one trip its "mission critical" because your talking about $50 for a container of it along with the adapter, seems pretty pricey since you will only use like 1oz maybe 2oz. but if you plan on doing further salt runs, then its a good investment.
i'd buy a $6 can of crc 6-56, or something similar, spray the engine, pump, hell, spray it everywhere except on the hull, and flush it on the hose when you get back, then maybe a nice run up a fresh water river, and fuggadaboutit.