Why duo boost needs no account sharing
In a classic boost, someone else logs into your account.
A duo boost avoids that: you stay logged in, your partner plays from their own account, and the only thing shared is the duo queue.
The trade-off: you play every game yourself, so progress depends on your schedule and on how well you play together. If you want to keep control of your account and learn along the way, duo is the option to request.