I know I am going to catch crap for this, but here goes anyway.
That looks so slow and clumsy. Every time I see military breaching doctrine, I just see a bunch of men clumped together where one man in an upper story can hit them all without meaningfully needing to change aim.
I know my paintball time doesn't count as a substitute for military training, but having cleared a lot of rooms alone and with groups, and shot at people trying to do the same, I cringe at the official tactics. They reduce a group of men into effectively two men. They are all in the open, vulnerable, attracting attention, and sitting ducks. They are in each other's ways for firing lines and angles, and even with assigned aim points, one person can fluidly transition through all the aimpoints with practiced motions more smoothly than having 4 men trying to lean through a doorway, with two more behind them. All their jammed up breathing and shuffling in close proximity blinds them to surrounding movements too. At least in theory they train out the "it's the other guy's job" effect, but you still don't know how observant the other guy is, so you have to second guess whether he has his zone covered. Quicker to just sweep through and move on. I mentioned paintball time, because I used to play a ton, and frankly, it was common to have groups of soldiers, marines, whatever come play straight out of deployment in combat. They tended to block eachother's firing lines and stay clumped together. They were nearly always easy to route by myself or with a random kid that I trained up for a morning. I think these tactics have a couple points of merit, namely visuallizing the blind room before entry and coordinating where you will go once the action starts, and moving efficiently once inside. However, I think stacking so many men just outside the door is a lot of why the military calls doorways "funnels of death." They send 6 men to do what should be a 2 man job. the others should spread out and cover other angles.
but every variant of their protocols makes 6 men have the firing/observing ability of 3 outside the door, and maybe 2 as they pass through and outside the door the whole group is as easy a target as one man. Giving them a hokey unreliable shotgun to fumble with just exacerbates all that by extending the time, and killing any surprise they may have.
Now feel free to tell me I'm ignorant and disrespectful, but that's my experience. I've watched a lot of these, read a lot of manuals, training presentations and the like. They all have that problem. Clumping people together in the open. I honestly think this training gets people killed.