I have to admit that I don't know as I've never used one. Combing daily every dog I've had is always enough to reduce noticeable shedding. Using the comb to the best effect is important though, lay it flat against the dogs coat and work it through at no more than a 45% angle. Done regularly and properly you will have no need to resort to anti shed preparations. If it is still a problem you may find the dog is lacking in all round nutrition, excersise or mental stimulation. If I sounded harsh I didn't mean to, honest! Quick fixes for dogs are just that - you are treating the symptom rather than the cause. Even if anti shedding stuff works you are non the wiser why. If nothing else the satisfaction of a "sorted myself" method is worth more than the money spent on "Sorted by someone else for reasons I don't understand. What is in this stuff anyway?"
I have tried to look at these products, sprays, water additives and food supplements with a view to help owners and really quite serious problems with shedding (their dogs had the shedding problem, not the owners,usually!). I have never used one as there is always an answer.
For these products to work they have to do one of three things; give the dog the supplements that his diet is lacking
stop or inhibit natural and healthy hair loss
make shed hair less noticeable to the owner by colour or disintergration