PawPaw summed things up fairly well on enjoying your new shotgun.
I have a new Mossberg 500 Special Purpose, the one with the teeth on the end.
Noticed that was the same thing you posted on your other thread
(the one with the teeth on the end).
That is a door breaching attachment which most civilians find no use for in a HD shotgun and usually end up removing if possible. Just an extra doo-dad that adds unnecessary weight.
To each their own but you'll most likely find a few more things to remove as well once the newness wears off and you want the best handling HD shotgun.
There was a very wise and respected 'shotgun' guru that when asked by new shotgun owners here on this forum what they could add to their shotgun for HD...."Wear marks" was his answer.
Have fun with your new shotgun. Put as many rounds downrange as you can. Learn its capabilities running different drills. And if possible, find and take a shotgun HD/SD course. You'll get more for your money then buying add ons which more than likely, you will later remove.
As for hard hitting,penetrating slugs...try some Brenneke KO's.