I went the 5.56 specific route when I bought mine and have come to find, it was a mistake. I should have gone with a .30 caliber can instead. A lot more bang for your buck with just one tax stamp.
I have an AAC M4-2000 which is 5.56 caliber specific. It has a quick detach type mount and works well, and I can shoot it for a bit without wearing hearing protection without any problem. Theres basically no muzzle blast, but you still get the sonic crack downrange, and theres nothing you can do about that.
When you look into the baffle stack, its pretty amazing how well it actually works, as its really not all that big, and the flash suppressor mount takes up the first half of it.
To give you an idea as to how well it works, my ears are shot (double hearing aids) and I cant shoot a 22lr from a rifle without protection, or Im about deaf for a couple of days after. I can shoot one of my AR's from my semi enclosed carport shooting 5.56 using the suppressor, without protection, and it doesnt bother me at all.
That said, I still normally wear hearing protection when I shoot with it, as if Im shooting a lot (anything beyond 50 rounds or so), my ears will start to ache and deaden a bit, especially after.
Where I found I screwed up was, my son picked up an AR in 300 BO, and bought basically the same suppressor I have, but rated for full power 7.62x51. His uses the same flash hider type ratchet mount as mine, and will mount right up on my guns. The suppressor is just a tad bigger, but its also noticeably quieter than mine when shooting 5.56 through it. Subsonic 300BO out of it is almost movie quiet.
A lot has changed too since I bought mine about a decade or so ago. There are a lot more choices and some are multicaliber from what Ive seen. If youre just going to get one though, Id consider at least looking into going up in caliber for the versatility.