Sherab ji
Perhaps, I can provide a context for the Psyche of the Golden Shield website, and informationm to the best of my ability. The site is operated by 3HO Sikhs (and I think they be located in Holland -- not sure about this though). You can also see how many "new age" and Indic elements are part of the site. All sorts of things are available.
I came to Sikhism via Kundalini yoga. It was never my intention to be part of an organized religion at the time. Chanting the mantras you see on the Table of Contents are part of kundalini pratice "as taught by Yogi Bhajan " (I love that phrase). Before a session there is chanting of - ong namo guru dev namo. During a session many different chants are used. During some kriyas there may be chanting. At the end of a session as well. Two things to point out that may be interesting to you.
Some of the mantras pre-date Sikhi and are actually Sanskrit chants pre-dating even the Brahminical period in India. Others are in fact verses from SGGS. It is a mixed bag. Because Kundalini yoga is ancient and Yogi was a Sikh. So for 3HO Sikhs there is a mixture of traditions. Just as India herself blended many religious and cultural traditions over the ages.
Now a person can practice Kundalini yoga and not be a Sikh (in India most are not Sikhs). And a person can be a Sikh and also practice kundalini yoga (as for example, 3HO Sikhs). But the value of the mantra is said to be in the vibrations that are triggered by each syllable. So different mantras, which are different combinations of syllables, call up various vibrations. The vibrations are believed to align you with specific results because of their psychic energy. Many new age practitioners - East and West, Sikh, Hindu, Christian, and others -- believe that these vibrations have influence on events in a person's life.
I try to keep an open mind. This is however one of those yogic concepts that i have difficulty with. My biggest problem was chanting mantras with obvious religious content when clearing my chakras or doing a kryia. It seemed wrong for me. After a week immersed in Sikhism I was relieved to discover that I could be a Sikh and didn't have to invoke a tranquil home with a mantra. But that is just me. For someone else it has deep significance.
In spite of everything I do find myself repeating the gurmantar many times a day. One does get results with that one. Anyway, I like what amarsanghera has to say.