Have some very limited (and somewhat dated) experience with this group. When I was in University (in the Netherlands) they were offering "yoga and meditation" classes in the univeristy building. It was one bearded monk-like guy dressed in Indian robes with a guitar and we did some simple yoga exercises and singing. I remember singing "baba nam kevalam" for a very long time and going into a very pleasant trance (this practice is called 'kiirtan'). The monk also gave some basic teachings on yogic living including food practices. He ate mainly sesame seed pate and recommended it. He also talked about orphanages they were running in Romania. Spiritually it seemed quite 'clean', no undue manipulation or fishing for followers or cash. The classes were free. This was about 15 years ago.
Years later, doing a internet search on them, I found out they were suspected of being involved in arms and drugs smuggling in South-East Asia. It then seemed like a very shady organization. There were also lively discussions on them on another forum where a lot of quite fanatical group members participated.
On the mantra BABA NAM KEVALAM, it basically means: 'Everything is an expression of one infinite, loving Consciousness'.
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Baba means "my most beloved One," Nam means "name of" or "to identify with," and Kevalam means "only." So the meaning of the mantra is "My most Beloved is the only One." The ideation is: "Everywhere I look, in everything I hear, feel, see, taste and smell, I perceive that one Supreme Consciousness which pervades all things."
Babanamkevalam.net