These are very unique guns, were made for a short period of time, and have features few S&W's have.
Notice the frame. It has the replaceable cylinder stop stud. That's a feature of the old style frame.
Note the hammer. There's no firing pin rivet. This gun has a frame mounted firing pin. That's a feature of S&W's new style frame.
S&W made millions of guns with the old style frame and the old style firing pin. Since 1996 S&W has made millions of guns with the new style frame and the frame mounted firing.
In their entire history, they made only a handful of N-frames with BOTH features of the old style frame and the frame mounted firing pin. Hundreds at most.
That's why this gun is so unique. It's one of the rarest revolvers S&W has ever made.