I built such a well... The concrete rings will just sloooowly slide down once there is room under them. If you dig evenly, they will just go down straight. Only a few centimeters at a time. This part does not feel dangerous. As a bonus,you can buy concrete rings with steps included, so you don't need to buy a 5m long ladder.

In historic well digging the walls needed to be secured with wooden planks or bricks and such after digging straight down. Huge risk of the walls falling in. This was a problem just generations ago... And all of the family had stories of grandfather's digging wells that collapsed and that the historic approach was dangerous.

With concrete rings, there is no danger of collapsing. And certainly, when placing a ring, noone should be standing inside!

But yes... - It becomes a little claustrophobic when this becomes deep. I stopped at 4.5m and got used to it by the time we came that deep. - I put a pipe in to blow fresh air to the bottom. This helps with the uneasy feeling of a possible bad smell - there is a risk of dropping a bucket on the head. Use a proper rope, a proper knot, a proper bucket made for lifting and stop when the guy above needs a break