There have been at least two separate fads of the sort of thing listed above which have reached some popularity and popular sales that I can remember.
Did they work? Well, in part, yes. But the bottom line is were the fish as healthy and long lived with the product as they were under their proper water conditions? the answer, as expected, is certainly not. Does anybody here see any real advantage in having a marine Angelfish and a freshwater Angelfish in the same tank? As I don't believe in mixed or community tanks under most circumstances, why on earth would I want to do such a thing?
Are there products which can make this even temporarily possible? Yes there are.
Are those products long-term as good for the fish as it's proper water conditions? You get three guesses. If you need that many you are in the wrong hobby. Of course they are not.
The real question is, when most folks are unable to keep fish well even in their proper water conditions, who are they kidding? The usual answer applies. They are kidding themselves.
For a real good question: How do you co-house one species of fish which all but never drinks water (any first division FW fish) with another fish which constantly drinks water (any primary saltwater fish) and hope to have their physiology and the fish cope? The answer? You don't.
This hobby is and always has been loaded with snake oil and "miracle" products. Some folks have even made a lot of money on some of these. Does that mean that they can or do work? Nope, it means that many hobbyists will believe anything, except the truth.
Normal physiologic responses are not just sort of inhibited, they are turned topsy-turvey and the normal physiology of the fish kills it. The products why play games with osmolarity have strong and clear limits. Without the use of such products, it just happens faster.