I recently paid much more then you did for a blue-4" that wasn't in as good condition as the one pictured, and it had replacement grips.
Why?
These were the last of the 1905 Hand Ejector/Military & Police revolvers that that the old "long action." At the same time they had a much better internal mechanical safety then pre-war guns. The later hammer block was developed at the end of World War Two and is still used today.
The "S" in the serial number denotes the use of the new safety.
The smoothness of the double-action in "long action" guns is legendary, and there aren't a lot of these so-called transitional guns around. The 5 inch barrel length is scarce, as is the nickel finish - if it's original.
You have truely lucked out. Take good care of it.