It is more delicate to edit than the normal VOCALOID engine. It can be used in conjunction with software suits such as VTalk. It differs from the normal engine, which focuses only on singing, it however works in the same manner of assembling phonetic data. Despite the fact it can now be commercially bought, much of the details of the engine are largely unknown. Its development was to further extend the usage of the VOCALOID software, making it feasible to use the software for private licensing.
Gachapoid and CV-4Cβ are two of the only voicebanks known named to use VOCALOID-flex. Further voicebanks using the software have not been confirmed. It was also used in part with the game Metal Gear Solid: Peace Walker. It was used for several mecha known as "Gear" within the game, the most notable being "ZEKE", though this was never confirmed to be the name of the voicebank. Ryuto's GachaTalk service ended on February 13, 2015. Parts of Vocaloid-flex were also intended for offer on the Y2 website NetVOCALOID, which was part of the VocaListener project. This lasted until April 28, 2012 when NetVOCALOID was shut down.