When sourcing Megger testers, prioritize Voltage Output Ranges (typically 250V, 500V, 1000V, up to 5kV or 10kV for high-voltage equipment). Ensure the device offers a wide Measurement Range (up to TΩ for advanced models) and high Accuracy Classes (±5% or better). Look for features like Auto-Discharge for safety, Polarization Index (PI) and Dielectric Absorption Ratio (DAR) calculation capabilities, and CAT IV 600V / CAT III 1000V safety ratings to ensure the device can handle transient overvoltages in industrial environments.