I've used both. They are almost exactly the same. The functions are the same, the layouts are the same, and from a functional perspective, everything is the same. The only differences are aesthetic (84 is more attractive), and the memory on the 84 is bigger, which means that the 84 is faster, too, but unless you're doing some serious calculations or apps, it's not really noticeable. The 84 also comes with more apps by default, and it comes with a cable and software so that you can connect it to your computer. It's a little pricier, but not by too much. If you want an 84, yes, you can absolutely get it instead of an 83. Functionally, they are the same. The keys are the same and everything; they just look different, but everything's in the same place, and everything works the same way.