Designing a usable checkout process is of paramount importance for both E-Commerce and M-Commerce success. Aiming to understand human-computer interactions during checkout and improve the usability and user experience of checkout tasks, this research work investigates the relation among users’ cognitive styles, and alternative checkout designs in terms of user preference and task performance. A controlled user study with 38 participants was conducted which entailed a psychometric-based survey for highlighting the users’ cognitive styles, combined with a real usage scenario with two variations of checkout designs that were deployed on standard desktop computers and mobile touch-based devices. Results suggest that human cognitive differences could play an important role in designing E-Commerce and M-Commerce checkout processes, and particularly users’ cognitive styles may affect the way users perceive and perform during such tasks.