Therabody's Theragun and Hyperice's Hypervolt are the two names most people mean when they say massage gun. Both brands sell a ladder of models, so the useful comparison is rung by rung rather than brand against brand.
The number Therabody leans on is amplitude, how far the head travels on each stroke. The Theragun Prime, Elite and Pro are all listed at 16mm. The current Prime, the sixth generation, is rated at about 30 pounds of stall force, the pressure it takes to stop the motor, with five speeds and a two hour battery. Its list price has moved from $299 to about $330.
Hyperice talks less about amplitude and more about quiet. The Hypervolt 2 Pro, which launched at $399.99 and is often discounted well below that, has five speeds running from 1,700 to 2,700 percussions a minute and a battery rated for up to three hours. Reviewers who have measured it estimate a shorter stroke than the Theragun's, and Hyperice does not make stall force a headline figure.
At the top, the Theragun PRO Plus is listed at $649.99 and adds heat, vibration and near-infrared LED to the percussion. That is a lot of money for features whose recovery benefit is far less established than a basic massage.
So the practical difference comes down to two things. A longer stroke reaches deeper, which matters for big muscle groups like the quads and glutes. A quieter motor matters if you use it in the evening next to someone watching TV. The Theragun's triangular handle also lets you reach your own back more easily, which a straight grip does not.
I would not pay for the flagship tier of either brand. The extra money buys a bigger battery, app features and attachments, while the part that actually does the work is much the same one rung down.
The short version: for deep tissue work, a Theragun Prime at around $300 is the value pick. If noise bothers you or your household, a discounted Hypervolt 2 Pro makes sense. Skip the $650 multi-therapy models unless heat and light are something you already know you want.