It's kind of hard to answer this question without knowing what kind of accessory it is. But yes, mainly small and lightweight are advantageous for all bike accessories. If it's something that has a screen, easy viewability is a must. When I'm riding down the road and I'm trying to read a display, it's hard to see tiny numbers which may be jiggling around. And yes, shock absorbance/vibration resistance is important, too, because things tend to get bounced around on a bike without suspension.