They're just seeds and other goodies compressed into a block - they sell similar ones for wild birds too.
It's the equivalent of a chicken candy bar so don't overfeed it, but when they're stuck inside due to weather, I like to put one in for a couple hours just to give them something to peck at.
Yup on food and water. I normally have the feeder in there anyhow so that's not an issue, for the water I just grabbed a chick sized waterer and refilling that daily was sufficient for my birds.
They won't be happy to be locked up, but a couple of days won't cause them to explode or anything...
Yup, this is what I meant. Lock them in there for at least a few days around the clock, as you should have enough room to safely do that.
Well, yes, if you don't clean it out at all. The few times I needed to lock my chickens in (to introduce to new coop, and for flooding) I kept up with my...