Asalaam O Alaikum,
Our beloved Messenger of Allah (saw) said on the day of Arafah, the Khutbatul Wida (The Farwell Sermon) he gave before his departure from this world. He (saw) said that the white does not have superiority over the black and the black does not have superiority over the white. Both are equal in the sight of Allah (swt) and both were created from earth/clay, both descended from the same father of all mankind Adam (a.s). Then He (saw) reminded them of the following Verse...
.... Lo! the noblest of you, in the sight of Allah, is the best in conduct. Lo! Allah is Knower, Aware. (Surah Al Hujurat 49:12)
What Elijah Muhammad preached I believe his successors are preaching is that the white man is the "devil". Ma'azAllah (We seek refuge in Allah) from such a concept.
It has taken a shape of a sect in Islam and the Messenger of Allah (saw) clearly said that ..." all 73 sects amongst the Muslims will be in hell fire except for the one and that saved one will be following the path of me and my sahabas."
The Nation of Islam does not promote and welcome brotherhood of Islam amongst non blacks especially white. And therefore they are detrimental for Muslims.
Thats what I know of them.