Dataset or DataReader? - Programming in C # .NET

Data-driven projects are heavily used in desktop applications, so I'm working on a library project where you save member records. I am using the 3 Layer Application method, it is very efficient and keeps the code clean. In the DataSet: I want a key ambiguity of the user both on the same, as the basis. Here is an example of the code I'm 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 TableAdapter .Fill () method, but using this method a lot does not make the application slow?

I wonder if the value of primary key will change if it is the same record. This could cause a lot of problems.