I would in no way equate what those who own that website with all Messianic Jews. There are doubtless those who would disagree with them.
I understand that within the area I live in, there are two Messianic congregations. I have been told that (second hand information) that there are huge doctrinal disagreements between them.
As far as I can tell, one of these congregations believes that Jesus came to restore the Jews back to their God given status.
(Sorry I don't know any of the details on this belief, or if it is an accurate understanding of what they believe.)
The other congregation disagrees with this.
I will say that I do know that whatever the major disagreement between these two congregations is, it is major.
Which would tell me if there is major doctrinal differences between Messianic Congregation in the area I live; chances are there a serious doctrinal differences in the movement as a whole.
Tom