I got this cleaner because it is the one I have seen recommended in numerous retouching forums, articles, and books. It is the kind of product you only use if you don't have a choice, if your original is unusable as it is. It's not something you would use on all photos you plan to scan, just when you must.
I have had pretty good luck with it using it on old slides and transparencies. It doesn't make them good as new (that would be impossible) but it does remove a lot of the mildew and fungus that would have made them totally useless. In the process, it saved me hours of retouching.
On prints you have to have a gentle hand. Pressing too hard or using too much solution can cause further damage. If used correctly, you do get improvement. If you can get them fairly clean with a blower, a microfiber cloth, etc., I'd try that first. If there is recognizable fungus or mold, you have no choice.
If it's a historic or essential photo, I would photograph it with a good, sharp, macro lens prior to attempting to clean it. Sometimes the damage that is there is so deep that simply rubbing it with anything at all makes it worse. Once you, at least, have a good photograph of it, then attempt the cleaning very gently. This is an extra step and extra work, but it is totally safe. (This is also the way to go if you have photos printed on honeycomb or other textured papers since they don't scan well).
Once you use the product, you can scan the image. I would never put an image full of fungus, mold, etc. on a scanner and risk contaminating successive images, so cleaning first is a must. (A good scanner glass cleaner is also a must. I recommend the Kinetronics Glass Cleaning Kit for Flatbed Scanners, also available at Amazon.)
Cleaning is not a substitute for restoration work, but it does take you to a point at which you can begin restoration work. I use Pec Pads that are lint free 4"x 4" little pads. This sounds small, but it's better for intricate work since you work on one area/problem at a time.
Another thing: this is a pretty strong smelling solution. I have asthma, so I use it outdoors wearing a mask. Between the mask, the lint-free gloves to avoid getting fingerprints on the slide or print, the tweezers or wooden skewers to hold the slide to the prepared work surface, working outdoors, and the fear of doing more harm than good, this process is a little tense and difficult.
But it is worth it. Anything that can possibly be rescued, has been rescued with this product. And, if you are gentle, don't rub, and don't press too hard, you (at least) don't further damage those things that can't be rescued with current technology.