I use my Simplex exclusively in the water. All summer in Lake Tahoe and other mountain lakes and rivers. It has helped me to harvest lots of gold and silver jewelry, and many silver coins. Never had a problem with it whatsoever. The SP24 coil moves through the water much easier than the factory coil. It seems better suited to water than The Legend, which I use exclusively on dry ground.
One thing I did to make it more comfortable was to buy the headphone connector plug on fleabay with a 3 foot set of wires already molded in and waterproof. On the other end I soldered on a mini headphone socket so I can use any wired headphones I want. I clip that connector to my cap so the connection doesn't get wet unless I go in over my head (I try to avoid that). I really like the waterproof JVC earbuds with an over ear clip, also available on fleabay for $10-12.
If you look at my posts from the summer, you'll see that detector has paid for itself many times over, and several times in a single hunt!