Lifehacker has a great explainer on sous-vide cooking for you to check out, but the basic idea is that you seal the food in plastic bags, and then cook it in precisely heated water over a longish period of time, resulting in meat that is heated all the way through to a very precise temperature. It sounds weird, but trust me when I say that it works like magic.
The Instant Pot circulator doesn’t actually require an Instant Pot to function, and won’t integrate with one in any special way either; it simply clamps to the side of any pot just like the Anova. It also lacks the Anova’s wireless connectivity, which is mostly useless on the Bluetooth model, but is somewhat helpful on the more expensive Wi-Fi version.
That said, if you’ve been meaning to buy one of these things, $89 is a great price for a gadget that will completely change the way you cook.