The short version
Both travel minis. Hypervolt Go 2 is the premium Hyperice ecosystem at $129. Bob and Brad Q2 Mini is the PT-brand budget at $99 with longer battery + more attachments + slightly higher stall.
When Hypervolt Go 2 is the right pick
If you already use Hyperice main devices and want app ecosystem integration in travel form — Hypervolt Go 2 is the right shape. Premium brand polish at $129.
When Bob and Brad Q2 Mini is the right pick
If you want PT-brand credibility + longer battery + more attachments + lower price — Bob and Brad is the right shape. Better raw value at $30 less.