In my opinion, using copper is a very bad idea for aquarium use. Let me tell you why.
Copper is extremely pervasive. It can leech into any plastic in your tank - filter parts, hose, silicone, plastic or silk plants, even driftwood. It cannot be removed with washing, and often permanently ruins a tank.
You may never be able to keep invertebrates in the tank ever again. Even some sensitive fish can be killed by copper leeching into the tank from the plastics, years after its use.
Although copper has been used in commercial fish farming, such as that mentioned in the linked article, remember that these farms are only keeping one species of fish, multiple mortalities are not an issue, and they do not want any invertebrates in their ponds ever. In aquariums, our objectives are very different.
On top of all that, killing many snails at once with a chemical can cause a huge ammonia spike due to dozens or hundreds of rotting snails and eggs. Then you have a lot of work to find and remove all the snails before the ammonia kills your fish.
The freezing is to humanely kill the snails and ensure they do not infest local waterways after disposal. If they are dumped down the drain, alive, they can enter the sewers and potentially enter creeks, ponds and canals that way. Eggs washed down the drain can hatch and within weeks, cause a huge infestation in any body of water. These are an EXTREMELY hardy species, and extremely prolific. Considering the problems with quagga mussel infestations in so many areas lately, it's very important to ensure that all aquatic pests are dead before disposing to eliminate that risk.
