I’d agree with the “buy once, cry once” statement. You’re going to be waiting on the thing for ~ 9 months, to make an extra $200 over that amount of time you could save your empty beer cans and take them to the scrap yard.
You’re also going to end up with multiple cans over time, unless you have some weird single purpose like just for your home defense gun or a hunting rifle. I’d steer away from “one can to rule them all”, not necessarily saying don’t go with a .308 can for the first one.
Anything that’s going to be durable enough for hard use on a 5.56 SBR and also large enough to reasonably suppress .308 is going to be a big, heavy tank that you‘re not going to enjoy shooting much. I’d say pick one primary purpose and then consider versatility with other guns second, don‘t try to fit anything and everything.
I like Dead Air cans, but there are plenty of other great brands. Their Wolfman can is crazy versatile, though not rated for .308 or an SBR in 5.56. I use it on 14.5” and 18” 5.56, .300 Blackout, 7.62x39, and 9mm. It pairs well with with something like a Nomad for your other guns, which is probably one of the best “first can” choices. I have a Sandman S that pretty much lives on my 11.5” 5.56, and I just got a Nomad Ti for my bolt guns, and .300 Blackout.
