I can only tell you what I remember from my own experience. The pastor of the Messianic Congregation of which I was a member, is of Reform Jewish parents. His wife is of Jewish parents, possibly Conservative. The pastor (rabbi) had a ‘conversion’ in the seventies, which he would describe as being of the Spirit of God.
Most of the ‘Messianic congregations’, but not all of these sort of congregations, have Jewish converts to Christianity as their pastors, (rabbis) who have had some sort of ‘conversion’ to the gospel.
Most of them would probably think of their ministry as being mediators between mainline Christianity and their own people of Judaism. They are usually engaged in fostering appreciation for the Jewish roots of the Christian faith, and also being good ambassadors for the people of Israel, eventhough most people of Israel and of the U.S. probably think of them as being disenguous ‘missionaries’.
Are they perfect? No, they are very human like the rest of us. If they had the holy Eucharist, like the Hebrew Catholics, I think they would be more complete. For this reason, it has been my experience that disallusionment causes a significant number to sort of ‘pull back’. I call these the ‘true believers’ who want the all of G-d in their lives, and a sure foundation in which to serve G-d. Many times they join other Protestant congregations, or even the Catholic church.
Here is a website regarding possible numbers:
bethadonai.com/FAQ_number_jewish_believers.html
God’s peace
micah