When a cryptosystem is described as 'effective,' it means:

An effective cryptosystem should indeed be easy to use while providing strong security across various keyspace values. This means that users can implement the system without encountering significant barriers or complications, making it accessible and practical for a wide range of applications. The ability to maintain effectiveness across all keyspace values ensures that the encryption remains robust regardless of the specific keys in use, thereby enhancing overall security.

In addition, the complexity of a cryptosystem should not hinder its practical application. A system that is overly complicated or requires advanced technical knowledge may limit its usability and, as a result, could lead to improper implementation or use, thereby undermining its security effectiveness. Therefore, the hallmark of an effective cryptosystem is one that balances ease of use with strong security features across its keyspace.