I came here and registered (my first post) because I was looking for accesories for this particular gun and found this thread on google. So I'll post my experience.
I have the 4" SS version of the GP100 and it's been a great gun. Heavy well built construction, Easy to handle, very well balanced, big stopping power, has never failed and not a bad recoil either. Plus you can put all kinds of cheap 38 rounds through it just plinking for fun. I love mine.