While the Micro Fence Edge-Guide has been improving router functionality for 30 years, I only discovered it a year ago. The Edge-Guide is precise and impeccably machined. You specify your router model when ordering, so the appropriate pins and mounting bar come in the box for a perfect fit. It brings accuracy to nearly all hand-routing operations, especially joinery.
I use it mostly to rout mortises. Mark the center of the mortise and butt the provided fence against the workpiece. Roughly center the bit over the mortise, and lock the lead screw. Dial in dead center by turning the adjusting knob (clockwise pulls the bit toward the fence; counterclockwise pushes it away), and then lock the lead screw. The Edge-Guide also excels at cutting dadoes for shelves in a cabinet, say. Measure your shelf stock with a caliper, rout the dado using the Edge-Guide and an undersized bit, and then measure the dado. Subtract the difference and adjust by the thousandths with the micrometer dial. It’s reliably accurate, repeatable, and a joy to use.