The brighter 135mm lenses (f2, f2.5 and f2.8) may deliver better performance but one big advantage of the f3.5 lenses is size and weight. They really are small and quite light. One disadvantage of these lenses is that you have to mount them using an adapter and these can make the lens seem rather large as it can add 2.5 to 3cms to the lens length. Doesn't sound much but it's a killer for some people. These systems are small and the whole point for some users to use the these systems on vacation etc is the size and weight. I fully agree with them but I enjoy using these legacy lenses so much the I'm willing to pay the price.