I am not equipped to answer for the Copts on this matter especially on the matter of differing rites. As far as I know the Copts usually celebrate their liturgy of St Basil whereas the BOC have opted for a diiferent rite. You need to ask Fr Peter why.
Although there are examples of liturgies in English with a few Coptic responses, I believe Bishop Angaelos is having the entire thing in English thereby making it available to English people as well as anglicised Egyptians (Why don't the Armenians etc do the same-don't they care about us atheistic Brits?)
The BOC church calls itself a missionary church and indeed with some justification it is especially seeing the efforts of Fr Peter and Fr Simon in spreading the faith. As has been said the more missions the merrier.
As far as the Greeks are concerned, they do have Saturday liturgies in some parishes on a Saturday but so far no one has started a Greek missionary movement to attract the natives or interest them.
The parish I attend has several catechumens, liturgy is entirely served in English (the only Chalcedonian church in London) and it calls itself missionary.
So the Copts must be congratulated .
Actually the fact that the BOC uses a different anaphora than the Coptic Church really has little to do with the question of rites. There is an article by H.E. Abba Seraphim on the BOC website if you want to know more about the reasoning. But if my priest prays St. Cyril's Liturgy while the priest in the next city prays St. Basil's, or if my priest prays St. Basil's while the priest in the next city prays St. Gregory's, this does not mean we are in different rites, we are all still in the Coptic rite. On the Other hand, when Ethiopians pray the Liturgy of St. Basil, still they are using the Ethiopian rite, with its hymns and variances, not the Coptic rite.
The BOC uses substantially the Coptic rite, which it has adopted over time since being received into the Coptic Patriarchate. All the Liturgical services are the same, baptism, weddings, etc. Even the Eucharist is basically the same, just with a different anaphora. However, elements of the rite have been modified in order to be suitable for Western culture. Instead of singing the doxology tunes of the Copts, a western tune is used, etc. This is important, because while the Coptic Church is my Church, it will never be the Church of my parents, or of any large part of my country. Most people will never get past the foreignness of the Church long enough to appreciate the truth of Orthodoxy. Some even see it is unpatriotic, selling out and joining a foreign organization instead of one from home.
Yes, the Copts are to be commended for using English, but only commended in comparison with other groups who have moved more slowly, not in comparison with historic Orthodoxy, which has adapted to the culture of the region and preached the Gospel, rather than becoming an Ethnic club that retains the ways of the old land. It seems strange to accept the BOC, and then at the same time set up English missions with Coptic tunes and customs. Yes, the BOC is very small. But maybe if the Copts supported them as the mission in England of the Coptic Church, so that their priests did not have to work hard at secular employment to support their families, they might be able to support more churches, and reach out more quickly.
In fact, what the Armenians are doing can be considered quite proper. Each jurisdiction should not set up an English mission, following the rites of the jurisdiction, as if we actually were separate Churches. If the Copts are providing mission to the English, then it makes sense for the Armenians and Ethiopians and Indians, etc., to have parishes serving their own people, but to not duplicate the efforts of the Copts, allowing the oneness of the Church to be proclaimed. In fact, as second, third, and fourth persons of each jurisdiction become less connected to the lands of the parents, and more to their new home, it would make sense for them to migrate naturally to the Oriental Orthodox Church of that land, rather than to set different OO Churches of that land. The ethnic parishes would decrease as the local ones increased over time, though there could always be ethnic parishes as needed to fulfill the needs of more recent immigrants. The cynic in me doubts this is the motivation for the other groups hanging back, but who knows.