If you are on a marina. the best and cheapest solution [ pun not intended] is to fit a bypass on your intake. I have one, and I simply run a bucket of fresh water through the engine before leaving it. Any residual salt can dissolve in the fresh water, and the heat exchanger doesn't get clogged.
For your question, I can't imaging that the commercial products could cause harm, they would be up for thousands if they did.