Won't that add extra weight, length, and less noise suppression than a dedicated 5.56 can like the m4-2000?
Not much and you can save a lot of money buying 1 instead of two. Less than 3 ounces added in weight, about an inch added in length, and about 3-4dB louder on a 5.56 host over the M4-2k. All 3 things you'll likely never notice. That includes an all inconel baffle stack and end cap and commonly available flash hider and muzzle brake mounts for 5.56 and 308 cal firearms. If you want to save some money, the 762-SDN-6 is where to do it.
762-SDN-6
Weight: 19.85oz
Length: 7.66"
Length added: 6.10"
Diameter: 1.5"
M4-2k
Weight: 17.1 oz
Length: 6.625"
Length added: 5.10"
Diameter: 1.50"