Infrared (wavelength, intensity) Ensure it actually emits enough heat to penetrate muscle tissue (not just superficial warmth)
Vibration / tapping modes & strength settings To adjust intensity so it's comfortable yet effective
Safety & certifications Certifications such as CE, RoHS, or other safety marks; safe temperature limits
Build quality & materials Durable plastic / ABS, good insulation, ergonomic handle, heat dissipation
Power source & cord length / battery Corded vs cordless, length, voltage compatibility
Head attachments Some come with different heads (flat, nodular, curved) for various body parts
Heat control / auto shutoff To prevent overheating or burning the skin