There is no problem with IS mounts, once you have the caliper set up in the right place, you can take it off and put it on again, and as long as the washers go back in the right place, the caliper will return to it's original position. When I had post mounts, I would spend ages trying to get the caliper in the right place, because when you tightened the bolts up, the b*****d thing kept moving. There is nothing wrong with IS, so whats the point in changing.