Editor recommended because this is the officially named Prestige Attachment for RK-9. It is not labeled BEST. Tradeoffs are quoted from official launch copy.

RK-9
UnderbarrelMFS Ironlung HandstopReach maximum Weapon Level and Prestige the weapon.
Stackable attachment that improves fire rate through reducing burst cooldown. Significantly reduces recoil when firing but removes the ability to auto burst. Provides flinch resistance but loses ability to hold breath.
Attachments 1
- UnderbarrelMFS Ironlung HandstopReach maximum Weapon Level and Prestige the weapon.
Stackable attachment that improves fire rate through reducing burst cooldown. Significantly reduces recoil when firing but removes the ability to auto burst. Provides flinch resistance but loses ability to hold breath.
Alternatives
- Base weapon / no prestige attachmentKeep the base gunsmith path if you do not want the official prestige tradeoff quoted above.
Evidence basis: Source
For streamers: add this as an OBS Browser Source — stream widget
Recommended · bo7-rk-9-prestige-launch