With the stressful competitiveness in our rapidly evolving society, people nowadays eagerly seek ways to enhance their self-awareness, exploration of the meaning of life, and the pursuit of happiness; therefore, Mindfulness is increasingly needed. To fulfill this growing need, a variety of mindfulness-practice products have been developed to provide real-time biofeedback of one's psychological and physiological health conditions, thereby helping regulate mindfulness practice in the pursuit of happiness. In this paper, we propose two design criterion dimensions (vertical and horizontal design) for a mindfulness biofeedback interface (MBI), through which we compare current popular product designs. Based on our analysis, we suggest that most MBI designs are generally good in the vertical design of MBI, but perform poorly in horizontal design. We also discuss the future challenges and opportunities of MBI design.