I have the palm swell grips on my early 4506 as well as my 1006.
These grips were developed for the FBI to be used on the 1076 pistol, which is the shorter barrel frame mounted decocker version of the 1006.
I bought mine from Midway at @ $18 each a while ago. These grips had been unavailable anywhere until recently. In my opinion they are the best of the three available factory options for the 45xx/10xx series.
Yes there is a gap between the grip and the frame on the left side where the decocker would be, it is not too obvious and does not trouble me in the least.
Here is a photo of my 645 marked pistol with the grips.