Disaster bushing for bearing failure and personnel protection. The smallest cross section possible to maximize the room in the narrow stuffing box. You need this room for radial shaft movement and for some place to centrifuge heavier solids in the liquid Cartridge designs for open impeller adjustment and ease of assembly. Be sure the cartridge is sealed to the shaft or sleeve at the inboard end. Outboard sealing can let solids penetrate between the seal sleeve and the shaft making the seal removal difficult Split designs for easiest installation and to avoid re-alignment between the equipment and its driver.
Glued elastomers are never acceptable.
The glue will cause a hard spot to form in the elastomer causing the dynamic seal to leak. Vibration damping, especially with metal bellows designs. Slotted or other forms of non dedicated glands for maximum flexibility. Rotate the fluid in the stuffing box rather than have the seal components rotate through the fluid. This is especially important in metal bellows designs because of their thin plates.