I mentioned earlier that they are usually thrown from cover. The other way they are employed is through windows on a "bang pole" which is a 15 foot plus metal pull with a contraption at the end to deploy the flashbang and a punch to break the window.
They are generally thrown from cover, usually directly following a door breach with a ram or shotgun with breaching loads(fairly uncommon in the PD world). You don't really want to peek first or stay looking because they go off fairly quickly.
Like I mentioned, taking a known armed felon at his residence with a no knock warrant is stupid. Take him down somewhere else where you have the advantage. Let him get in a car, tail him, when he gets where he is going deflate his tires and then catch him as he comes back to the car. Much less likely he is gonna have his AK on him when you catch him coming back to the car from McDonalds...
I am completely against no knock warrants outside of a few extremely limited circumstances that rarely occur. It is dangerous for all involved. If someone breached my front door at 2am they would be receiving rifle rounds as soon as I picked mine up.