The particular formulation of chemicals to be applied to plants is very important. The form (powder, liquid, suspension, flowable, pellet) the exact chemicals used to supply the intended active ingredient have a very important effect on the chemical working or not, and very importantly for plant applied chemicals, the phytotoxicity of the applied chemical to the plant. Just because it contains copper doesn’t mean it will work, or work as well, or burn/not burn the plant when following the application instructions exactly. A number of pesticides have had their formulations changed because the chemical worked but burned plants. The new form is intended to be more active or stay on or in the plant longer (not wash off, release slowly) but not burn the plant. Earlier cheaper chemicals may have worked well but had a nasty habit of burning plants or poisoning people, frogs, butterflies, birds pets you name it. Newer chemicals have been formulated to be safer to plants animals people, the environment. And certain older formulations May have lead to resistant insects and diseases. A change in formulation May be more active against resistant strains or be able to penetrate cell walls and stomates. So it becomes very important to read labels and literature to find out details, warnings against treating certain plants because of burns. An important reason why some formulations get changed is because of the during and after safety considerations. Many pesticides have REI’s or restricted entry intervals and different warning words and danger levels. Lots of copper products previously had 24hr REI and strong damage to eyes and skin is exposed during application and for 24 hrs after spray. Many plant nurseries can’t close down an area for a whole 24 hrs after application, so a changed formula that kills the target but is ‘safer’, allowing normal entry more quickly is very valuable to a nursery. Also in the age where we desire less residues on our food crops and want organic products to eat, newer safer less residuous (just made that up

) pesticides are highly desirable and demanded by governmental organizations. Copper is considered ‘elemental’ to some degree, did you know that some harsh copper products are allowed to be used on ‘organic’ food products? Also other interesting compounds that have been defined as ‘found in nature’ so can be used on organic products
So the more basic or simple copper product more widely available may be effective or cheap, but may be more dangerous to plants and living things than newer versions. Tons of money is spent on creating, testing, making legal in a state or country. And if it doesn’t really work, it’s not likely to be brought into the market. This is for pesticides and chemicals that have very strong restrictions on being allowed into the market to protect the total environment (butterflies, bees, frogs, water supply, people.....). Things that don’t need to have restrictions like common household or fertilizing products, can very well be ‘snake oil’ things and not be helpful at all. As long as they don’t have poisonous effects, they don’t make unprovable claims of health then they can exist without working
It’s likely all of those copper fungicide products work to some degree, just how safe are they? And you have to read the label always. Does one form of copper list to be used against the disease you need treated but not others? If not on the label, then it’s not likely to do much good, or only effect a little. A certain chemical may say ‘don’t use on orchids, damage’ or another May say ‘orchids are included in the tested and found safe list of target plants’. If you are an orchid business and you use a chemical listed as ‘don’t use on orchids’ and there’s damage, it’s your fault. Use not according to the label can incur strong legal liabilities. So always read the label. It will tell you if you should use or not