A brush type shoe that moves up and down with the router will ride right over clamps and other protrusions as long as the protrusions are not higher than the flexible portion of the shoe. If the work is flat and the work path doesn't approach clamps the fixed height shoes appear to do a nice job. My 3" brush is far from vacuum tight but moving a large volume of air compensates for that pretty well or at least I believe so, dust at the micron level is hard to see

Different horses for different courses ?