I've used a magnifying glass for first aid a couple of times (small splinters are easier to remove when you actually see them). For most purposes 2 - 4 times magnification is enough. when the magnification is too big the image gets shaky when have a look at something. I carry a fresnel lens as they are small and leightweight. They take almost no space in my wallet. I'd rate it more usefull for urban EDC than compss (which carry anyway).