Ultra-low magnetic field sensing is rapidly emerging as a technology in various applications, providing a non-invasive and instantaneous method of data acquisition. The increasing availability of improved or innovative types of magnetometers promotes the need for a benchmark metric. This contribution focuses on the evaluation of single magnetometer systems that detect magnetic fields in the femtotesla range and are usually used in a magnetically shielded environment. For assessment, a Device Alignment Actuator system is presented that enables an accurate 3D alignment of the Device Under Test around a single point within a known, homogeneous magnetic test field inside the highly magnetically shielded room, called BMSR-2.1 at the Physikalisch-Technische Bundesanstalt Berlin, Germany. The defined benchmark metric includes several key parameters, such as frequency response, amplitude stability, frequency stability, and directivity, to name just a few. These parameters are demonstrated using several commercial state-of-the-art optically pumped magnetometers (SERF-OPMs) and compared to the reference system based on superconducting quantum interference devices, which remain the gold standard in magnetometry. This approach ensures consistent evaluation across different magnetometer types, provided they operate at room temperature and fit within the evaluation platform. The platform can also be adapted for multi-channel magnetometer systems.