It would be more flexible to store an std::function rather than a raw function pointer.

If flexibility is not required (for example, only a small number of pre-defined functions are expected as actual parameters), then it is better to restrict the possible input values: the parameter should be some kind of identifier for the method, for which the function stores the corresponding function pointer in the Method field.

If an arbitrary function should be accepted as Method, I suggest to use std::function, which allows much more options for the user code to set Method (e.g., lambda expressions, bind expressions, member functions).