Apparently It makes a 5.56mm sound like a .22...
Suppressors on automatic rifles firing a 5.56mm round will reduce noise by 30-40 decibels. This means each shot will sound more like a 22 caliber.
Yeah right. They are still loud enough to hurt and probably cause hearing damage with sustained use. Firing from under cover, or inside a structure where there is sound reflection is no joke without ear protection.............go on ask me how I know.
On 5.56mm with military ball ammo suppressors take the edge off the bang, but do not eliminate it.
Then it comes down to barrel length: The longer the barrel the more the bang is reduced, so for a bog standard 16" barrel they are more effective than some of the 14" barrels that are starting to see the light of day in ordinary units. As for the !2" and 10" barrels used by the speshul ones the benefits are better than marginal. Depending on the internal design of the suppressor you can more or less eliminate the muzzle flash which is a tad handy during low light engagements. If engaging at ranges in excess of a couple of hundred metres with a suppressor fitted it can leave the enemy wondering where you are.
Personal experience: I have a 10" AR, when firing it there is a football sized muzzle flash, and it is loud. With a suppressor fitted there is no muzzle flash, and it slightly less loud.
There are plenty of septics who own personal suppressors and at around 50m to a 100m away on the range it is not unpleasant and you can be left wondering where exactly the noise is coming from. 200m away and you really need to be looking for who is firing with a suppressor. If they were in cover they would be difficult, but not impossible, to ping.
I could not see who they had bought the suppressors from, in the way of all procurement though I can guarantee that they are not state of the art and more designed for longevity and to be marine proof. There are some good designs out there at the moment as there is a fair bit of research going into the subject. A couple of hobby enthusiasts on a forum I visit have come up with a very good internal design which reduces the noise of the bang by around 30% more than commercial suppressors using standard ball ammo. The results are repeatable and effective enough that they have taken out patents on their widget with a view to going into production.
Suppressor life is a variable based on the materials the suppressor is constructed out of. There is an adage in the suppressor community that you can build a suppressor out of most materials, but the better the materials (more expensive) the longer the suppressor will last. Make one out of aluminium and you will be lucky to have it last a 1000 rounds. Move up to stainless and it will go for a few thousand rounds, maybe even 10,000. Start to add titanium and inconel to the internals and it should last 10,000 rounds, possibly more (put into context; an AR is mooted to have a barrel life of around 15,000 rounds). Much depends on how well the suppressor is cleaned, are you firing single shots, or emptying a magazine in 2 seconds regularly.