Qevs won't make a noticeable performance difference with mech sliders and hinges, but they may have a subjective impact on the cycling action and feel. I think mechs with qevs tend to feel crisp and snappy. My mechs without qevs feel more smooth and soft. Some guys like qevs on mechs, some don't. Some guys just like the aesthetics of mechs with qevs. I like them when done well.