What you pay
The Hypervolt 2 Pro sells for $359–$399, the Theragun Pro $499 and up. The Hypervolt is the cheaper by a clear margin.
Noise and battery
The Hypervolt runs much quieter and lasts longer per charge. The Theragun is louder and its battery shorter, though swappable for $109.
Force and fit
The Theragun hits deeper for deep-tissue work, which is why pros reach for it. For most home users the Hypervolt covers the need for less.