Howdy
The Perfected Model was the last Top Break S&W revolver to be introduced. Made from 1909 until 1920, 59,400 were made. A very few did not have the thumb piece cylinder release, the great majority of them had both the thumb piece latch and the Top Break latch. I have read that the reason for the double latch system was because a bad guy could reach over and disarm a traditional Top Break by lifting the latch. Personally, I think that is a lot of hooey.
The Perfected Model was the only Top Break revolver that S&W made with the trigger guard integral with the frame. In fact, the frame profile pretty well mimics the 38 Military and Police revolvers that were first made in 1899. The Perfected Model was the only Top Break S&W revolver to have the side plate on the right side of the frame, just like a modern M&P. I have never figured out why Smith made these, the normal Top Break system worked fine for many years. The Perfected Model is awkward to operate, having to manipulate both latches at once.
SCSW says barrel lengths were 3 1/4", 4", 5", or 6". Slight premium for the 5" barrel.