They are not made of copper, but of cheap brass.
In a sailboat, the crimp connections made of a brass alloy failed due to stress corrosion cracking right at the front of the shoe's bending radius. Therefore, I was looking for crimp connectors that weren't made of copper-zinc (brass), as is usually the case, but of copper, which is significantly more resistant to corrosion. Contrary to the description, however, the crimp connectors are not made of copper, but of copper-zinc. The price is therefore unreasonable.