JH Audio Angie dips below 4Ω at points. It's a niche case where <0.5 Ω is needed for output impedance much like the Hifiman HE-6 is for power required.
"Niche case" means "any" is inaccurate in the sentence "At 1.7 ohms, it is very low making it suitable to driving any headphone without changing its frequency response."