There are of course many things an Orthodox Christian might read concerning Prayer of the Heart. What I often suggest that people read first is a little book by Metropolitan Kallistos (Ware), called The Power of the Name. It is a superb introduction to the subject: short and to the point, beautifully written, and (of course) thoroughly traditional.

I would beware of “Hindu mystics”. I have never heard of the man you mention, but what you describe has all the trappings of the “New Age”: syncretism, a thirst for the paranormal, and a total absence of any sense of spiritual proportion. Jesus is of course perfectly capable of showing Himself, or speaking, to whomever He wishes. But I very much doubt He feels obliged to corroborate the transcendent unity of religions by making a special trip to rural Texas!

Keep in mind that Orthodox startsi (“elders”) have always cautioned their disciples against seeking experiences or placing too much stock in supernatural phenomena. One is to turn away from prelest (“charm”) and plan? (“wandering”) so as to remain exclusively focused on the One who is named in the Prayer.

Perhaps I should add that—mutatis mutandis—this is the advice you would get from traditional authorities the world over. The spiritual traveler must endeavor to detach himself not only from material distractions but from “spiritual” (in fact psychic) distractions.