The JET RSS50 is meant for printing abrasive materials, and such much stronger than a brass nozzle. The downside is slower printing speed due to the lower thermal conductivity of steel, compared to Brass (ca 60% copper).
WHY JET RSS? If you print a multi-hour object with an abrasive material using a brass nozzle, you will experience that the nozzle wears down while printing. This increasingly affects print quality until it becomes unbearable! JET RSS needs higher temp and slower speed! Steel conducts slower, but will not fail during a print!