When I got my first HW97 I opted to get the proprietary HW moderator at time of purchase. It's really not necessary but does take a few db's off (kinda sounds like a red ryder, slight twang with no "snap"). Only noticed the little sound reduction because a slight muzzle report would rebound/echo off the barn and/or shed while shooting off the back deck (without the additional can), never really noticed in open field. Pellet impact is much louder than a box stock HW97's muzzle report. Didn't bother trying to quiet my second HW97.
That being said, some find the need to quiet their AG's as much as possible for various reasons. As long as it doesn't effect the accuracy or risk pellet clipping, I say do whatever that tickles your fancy, floats your boat or get your jollies off. I will say an insert is cleaner than a can, but I'm not a fan of 3D printed anything past the muzzle...
