A model always holds more rights by not issuing a model release. If you are testing or shooting TF*, the purpose of the shoot is to produce images for portfolio use. Both photographer and model will be able to use those images for their portfolio even without a model release or a usage agreement. Many agencies do not allow their models to sign releases. My recommendation for agency models is to not sign a model release for testing. On the other hand, non agency models and photographers often have very different understandings of what is expected from TF* shoots. In those cases, I recommend both parties use a shoot agreement, a model release, and a usage agreement to avoid any confusion and mis-communication.