Decent round if you want a suppressed SBR, but for every other purpose there are better options for the AR-15.
The great thing about the 300blk that make it better than many of the other popular AR cartridges, is that ALL
you need to convert is a new barrel. (assuming an existing upper in .223) Thats it. Install it in the upper and boom, you have a 300 blackout. Cant say that about 6.5 grendel or 6.8 spc, since both require new bolts and special mags for reliable feeding.
Plus, since the parent cartridge is the 223/5.56, you dont even need to buy brass....
it might not have quite the trajectory or power of the other two, but the difference isnt much, not enough to worry about in my book.....