Daniel,
You asked your questions on just the right forum and you received some straight answers - period!

I have hunted with Parker double guns for going on 70 years and custom made double rifles for 15 years and I agree with most of the above. Personally, such crap as a de-cocker has no place on a quality firearm, shotgun or rifle. I de-cock my doubles with snap caps at the end of a hunt. A properly made and maintained rifle works as it should- another period!

Continue to shop carefully and you will likely be pleased with your purchase.

For an informative read, I suggest the Cal Pappas book, "The Double Rifle Primer" .