Although they were all stated to be incomplete by individuals, they`re very powerful even when compared to other robots and are quite possibly even be the strongest of there size.
Despite being called incomplete, if one looks closely at the story and characters you may see that they (especially Jiro) were actually complete in their own way.
In both the anime and manga, Jiro was the only one to survive while the rest died (ironically) at the hands of Jiro under the influence of the Submission Circuit.
In the tokusatsu they all survived in the end and defeated their common enemies.
Rei`s origin differs in the manga and anime while he did not appear in the tokusatsu.
In the manga, Jiro built him making more of a son and nephew while in the anime Komiyoji partially built him and was completed by Komyoji`s master making him more of a brother.
Although they technically have more brothers, these robots are unique in a sense that they are similar to one another in both appearance and name (with the possible exception of Saburo) as most of their siblings did not have free will (aside from Gold Wolf in his human form and perhaps Jinbei) or look nearly as human (in their true forms) compared to them (especially against Jiro who can be thought as Komyoji`s greatest creation).