Coffee Joulies are a novelty. As a coffee drinker I chose to go ahead and buy some when they were entered production following a successful kickstarter campaign.
I dropped three of these shiny giant coffee beans into my cup a few years ago. They have not come out since then. I run my keurig on 192º and use a 20oz Contigo cup. One Coffee Joulies displaces about .7oz each for a total of 2oz in my cup. That leaves room for the 2oz of honey that I add to my drink. I flip the cup over a few times and the coffee is now drinkable and sweetened just right for me.
To really extend the warmth of the drink over a long period, like during the winter when your coffee will be out in the cold, then you need to pre-heat the Coffee Joulies. Run them under hot sink water or soak them for 5 minutes in hot water. Then dump that water and fill your cup. You will have minimal immediate temp drop, so be carful because you drink may be hot. And hours later the drink will still have a nice warmth that would otherwise be gone. I like to swirl my cup at the bottom. The liquid will extract the remainder of the residual warmth from the Coffee Joulies.