The Illuminating Fan Brush by Real Techniques is reviewed by Christy in a video review. Christy mentions that she has tried the brush multiple times and likes it. She notes that it applies differently compared to her old highlighter brush, which had a bigger fan. However, she still finds the Real Techniques brush to be great and recommends it. The brush has a short fan shape, but it works well for applying highlighter. Overall, Christy's review highlights the positive aspects of the Illuminating Fan Brush, emphasizing its effectiveness and recommending it to others.