I'd say go for it!...I have one (fitted from new) and I think they work well...I'm always amazed at the Crap and Crud it dislodges after a flushing!...so it would follow it get's rid of at least most of the salt post Dunking!
Especialy good when used with a Power washer!...and I also find them useful for cooling the Brakes/Bearings with Fresh water before Launching i.e. after a long Tow.
Also have the Alloy Hub- Bearing protectors fitted,which seem to work well too....Anyway Towed this trailer in excess of 4,000 miles+ so far...with MANY Launches /Recovery's and thankfully no problems
And I do Check it regularly.