Not to be that guy, but it's not a silencer, it's a suppressor. Depending on the brand and design, and the firearm it's attached to, it reduces the noise around 20-40 decibels, maybe a little more. About what a good pair of ear ----- should do. An AR in 5.56 produces about 150dB at the muzzle, 130 or so effective dB at the ear of the shooter. A good quality suppressor should bring that down to around 100-110. You can get even more noise reduction with larger and longer suppressors, but then you're talking about a can larger than the firearm itself. Subsonic rounds are even quieter, but then you're losing a lot of bullet performance.

As JPW stated, it's not like Hollywood, a suppressed rifle still sounds like a rifle, just 20% or so quieter. Good quality suppressors start around $800 - $1,000 and can go a lot higher, the tax stamp is another $200. Not a big deal if you really feel the need.

Small sample size, but I know a dozen or so people who use them for hunting or the range, I haven't heard of anyone being denied a stamp. People I know who shoot with them are hunters who use them in place of hearing protection when doing a lot of shooting, or to avoid spooking other game when we're hunting. I'm not sure it makes that big a difference to the animals. I've tried one on a .22-250 for coyotes and prairie dogs, the noise reduction is nice but I'd rather not lose the muzzle velocity when I'm shooting at long range. The critters don't seem to react any differently.

If you're looking for hearing protection, in my opinion you'll get much better performance out of a high-quality set of reactive ear-----. They'll cut down the noise of gunfire about 30-40dB, and can be adjusted to still be sensitive to environmental sounds. With a bluetooth enabled set you can even listen to your playlist while you work a prairie dog town or coyote den. And you can get a high quality set for $100 or less. I can see where using a suppressor and ear----- together could reduce heard dB's even more.