There is one significant difference between the Glock and P11, and that is the frame, which is aluminum on the P-11 and a steel insert on the Glock. There has been no report of significant damage done to a P11 by the steel guide rod, although some users have had to polish the steel rod to reduce spring friction and eliminate frame abrasion. Kel-Tec CNC has taken a neutral stand on this issue stating that the polymer rod should last the life of the gun. They also state that the steel rod is unquestionably stronger. However, there is no apparent technical or reliability reason to use the steel rod.
Users can make their own choice.