Guttenberg only discusses equipment that he already likes if that is what you mean. I have never heard him give a negative review because that stuff is not what he reviews. The word "promoter" as you were using it seemed to imply that he is a paid lackey for some product. That is a rather disingenuous observation in his case.
I did hear him review the Holo Audio Serene and detected a slight note of reluctance in his voice. His friend Herb Reichert of Stereophile had given it a glowing review, and there I did notice Guttenberg giving an ostensibly glowing review that was still holding something back. That's the first and only time I thought I saw him looking mildly self-coerced to give a positive review.