When selecting a ferrite isolator, you must prioritize Frequency Range (MHz/GHz) to ensure it matches your system's operating bandwidth. Key performance metrics include Insertion Loss, which should be as low as possible (typically <0.5 dB) to minimize signal attenuation, and Isolation, which should be high (typically >20 dB) to protect active components from reflected power. Additionally, verify the Voltage Standing Wave Ratio (VSWR); a ratio of 1.25:1 or lower is standard for high-quality signal integrity.