The Diplomat Nexus fountain pen stands out due to its unique, patented sealing system that prevents ink from leaking, even when the pen is capped or during travel. It features a self-sealing eyedropper mechanism, allowing for filling with bottled ink using a medicinal eyedropper or ink syringe. The pen also boasts a large ink capacity and a solid, well-finished construction, contributing to a reassuring and infinite writing experience.