This article gives some information about them: They apparently were forced to convert to Christianity, but kept Judaism secretly. They received less attention than Beta Israel, and haven't left Ethiopia to Israel significantly like they did. They seem to, according to the article, keep many Jewish laws (perhaps all — it wasn't clear from the article). They also do some interesting customs I've never heard of others doing (e.g. smearing lambs' blood on doorposts for Pesach).
As for the question of whether they are Jewish according to halachah, I don't know. The article makes it seem that way, but it also says that they aren't recognized by the rest of the world.