I had an opportunity to fire a Keltec KSG 12 ga. shotgun with a suppressor attached this weekend while visiting Windham Weaponry. If you have a need to fire a KSG indoors, using a suppressor is the way to go. Without the suppressor, the KSG is incredibly loud even with hearing protection. The suppressor makes the sound more manageable, and it seemed to make the KSG even more accurate. I don't recall the make of the suppressor, but the staff reported that the suppressor costs more than the gun. In spite of the cost, I believe a suppressor for my KSG is on my shopping list.
We also had a chance to fire a Windham AR-15 set up for three round bursts. That was an interesting experience. I guess one of those will be on my shopping list too. I need to win the lottery!