Buddhism begins with The Truth of Suffering. That seems like the best point to get someone's attention, and is basically indisputable. The Truth of Impermanence is fairly easy to accept, because we see things change, and everyone dies. But the Truth of Not-Self - no separate, permanent self - is the major departure from Hinduism, and all other religions, as best I know. Realization of this truth amounts to nonduality.
If someone can realize Anatman then is this not basically the whole teaching? With the large number of Self-Inquiry groups and websites devoted to nonduality and the many interviews and books about it available, it seems like a more direct path to realization, and more accessible than Buddhism (in its many forms). Is it?
EDIT: I seem to be drawing fire for my phrase "the whole teaching". OK, disregard that but the point is: if you "get" Anatman, doesn't everything else have to fall in to place over time? With that one realization, you can realize everything, and without it, you will never make it all the way. Is that not so?