@Abetillo There's also the part that the water circulation caused by these units helps maintain an even temperature rather than having hotter water in one spot and cooler water in another causing uneven cooking. It's not necessary but does help. It's possible to just set water temperature via low heat or oven, or even hot water into a large cooler to maintain the temperature. The main thing is the precision, since you may want to cook a steak to 130 this way so that it's rare, but not cook it past this. And you don't want to go under this due to food safety. Also, when cooking sousvide, you want to remove the air from the bag to prevent floating, though there are some methods used to prevent floation for lighter ingredients.
Prior to my Anova, I used a crockpot and a temperature probe with a target of 138 or so, so the temperature variation wasn't an issue for me, but if I'm going to spend money on prime rib, then I want to make sure I get the temperature right.
The characters did comment that it looked like clay, so like everyone else, I do hope it's revisited with the sear afterwards.
There's lots of information out there on the Anova website, Chefsteps website, Serious Eats website https://www.seriouseats.com/2010/04/cook-your-meat-in-a-beer-cooler-the-worlds-best-sous-vide-hack.html and https://www.seriouseats.com/2016/01/first-thing-to-cook-with-sous-vide-immersion-circulator-essential-recipes.html and more