Dataset or Datareader? - C# NET programming

Question

Data-driven projects are widely used in desktop applications, I’m with a library project that saves member records. I’m using the method of Application in 3 layers, consists of a lot of efficiency and keeps the code clean. In Dataset: I want an ambiguity of the key user both in the same and in the database. Follow an example of the code I am using:

public int InsertMembro(Membro m)
    {
        string sexo;
        int key;

        if (m.MemberSexo == MembroSexo.Feminino)
            sexo = "F";
        else
            sexo = "M";
        //Insere na base de dados
        key = (int) usersTBL.MembroINSERT(m.MemberName,
            m.MemberRG, m.MemberEndereço, m.MemberBairro, m.MemberCidade, m.MemberNascimento, m.MemberTelefone,
            m.MemberEscola, sexo);

        //Salva os dados no DataSet
        dataset.Users.AddUsersRow(m.MemberName,
            m.MemberRG, m.MemberEndereço, m.MemberBairro, m.MemberCidade, m.MemberNascimento, m.MemberTelefone,
            m.MemberEscola, sexo);

        return key;
    }

Note that the record is saved both in memory and in the database. I thought about the method Tableadapter.Fill(), but using too much this method does not slow down the application?

I think about whether the value of Primary key will change if it is the same record. This could cause several problems.