The organizations are not connected, i.e. they do not cooperate, they are more like rivals, fishing in the same tank for the same kind of fish
They are very similar in a kind of parallel way:
each organization is founded by a catholic priest;
their original language and culture is ‘Spanish’
each is ‘led’ by a group of priests that trains a group of ‘lay’ Catholics to be Catholic leaders in society.
The general goal is to imbue society at large with Catholic values.
This involves winning over the political world, the business world, the press, the media, the catholic hierarchy, educational institutions such as colleges and universities, etc.: or influencing them to a considerable degree, or at least influencing them to the degree that they will not interfere with what the organization is trying to do, which is to influence society [sufficiently confused?].
To be able to recruit, train, influence, build, etc. etc. the organization needs a lot of money. Members and their families may contribute, special very rich benefactors will contribute, and schools and universities serving the upper social classes will generate funds.
‘Elitist’: both organizations basically aim to win over the more influential sectors of society and thus target the middle and upper social classes. They believe that ‘the revolution starts from the top’ and filters down. Helping the poor is usually cosmetic, in a kind of a CYA sense. i.e. to prove that they are Christians, charitable, good. Neither organization spends a proportionately large amount of resources or wo/man power helping the less fortunate. Their ‘poor missions’ can also be another way to raise funds from well meaning Catholics.
Both are secretive, in that they keep to themselves and do not mix freely with non-members or share information with those who may be unfriendly or unhelpful…they tend to infiltrate other organizations and take over quietly. [see controversy about catholic school taken over by LC/RC
Both have separate groups of male and female members: Men’s Section, Women’ Section, Male Youth Section [Jovenes] , Female Youth Section [Señoritas]. They also have a section for teens, boys and girls separately [The Legion/Regnum Christi calls this movement ECYD in Spanish]
They are different:
The OPUS DEI [latin for God’s Work] is from Spain, the Legionaries of Christ and the REGNUM CHRISTI [Christ’s Kingdom or Reign] is from Mexico.
The Opus is older by some 20 years. Their founder is dead. The founder of the LC is 82, the same age as the Pope and is still alive and running the organization.
The Opus priests are not so well known separately from the Opus Dei organization. People usually call them the ‘The Opus priests’ although officially they are ‘The Fathers of the Holy Cross’; whereas the Legionary priests are recognized as a distinct Religious Congregation [order] and their movement is called ‘Regnum Christi’ [the Kingdom of Christ].
Father Maciel’s first idea was to have missionary group of priests; the idea of having lay apostles came later. This is a bone of contention. We -the critics- say the ‘inspiration’ about training lay apostles came to Fr MM about the 60/70s. The official LC line is that it was there from the beginning. This is truly false. I do not know whether the OD founder, Escriva, had the idea of lay apostles from the beginning of his foundation.