I went for this in February 2020 in Tanjung Benoa, Bali. It was an excellent experience. There is another in Sanur that costs double.
Okay, first things first. If you are planning a seawalk, you will find two types of prices, one double than the other, and I found this not explained anywhere.
1. The higher priced one is a 1 hour big boat ride (seats around 100 people) from Tanjung Benoa port in Bali towards Nusa Penida/other island. You dismount the big boat on a big pontoon (floating anchored jetty of sorts). There is a fixed ladder from the pontoon to the bottom of the sea (around 10-15 meters). A big helmet is placed on your head, and you take all the time in the world to climb down to the bottom, while a diver in scuba gear supervises, and assists you. Then you walk for a bit, and climb up the stairs to the pontoon. They take underwater photos and videos and will try to sell these to you at an exorbitant price. The camera fees are postpaid, and this is completely optional. But your photos and videos are taken whether you will buy them later or not. They will also have several pairs of good boots that you will need to walk underwater in.
2. The lower priced one is a 5 minute ride in a pretty small boat (4 people), and you dismount on to a small pontoon. There is a small ladder of 3-4 steps, on which you stand while the helmet is placed over your head. Then the diver in scuba suit takes control, and will take you down to the bottom of the sea pretty fast. Then you walk for a bit, and you are then taken back to the pontoon by the scuba diver. Then the small boat takes you back to port. You will need to rent and take a GoPro style camera (also exorbitant price) which will be used to take your photos and videos underwater, and then given back to you to take to port where they will give your photos and videos and keep the camera. This is a prepaid system, so if you don't rent and take the camera beforehand, the guys over at the pontoon don't have any gear to take photos and videos. They have just one pair of plastic shoes for underwater walk, that is a tight fit for most people.
P.S. The GoPro cameras/similar ones they have, are really old, and take VGA level photos and videos. Don't expect these to have stunning quality that you can view on a 4K TV.
We did option 2, and the experience was good. They take good care of you, and co-operate and help fully.