As with every Festool product, after looking at the price tag, your first question is — is it worth paying that much money? You can certainly get a very capable miter saw for less. What you won't get is second-to-none build quality, an insane warranty and top-notch HEPA dust extraction.
If you have a small shop, as I do, I highly recommend the Mobile Miter Station. Not only does it provide a solid base when you're using the KS 120, but it folds up — with the Kapex attached. This means it doesn't take up much space when you're not using it, but it can be ready for use in about 15 seconds.
I also recommend the Cart Extensions. They take up almost no space when not it use, set up quickly and provide a solid work surface for cutting long boards. The integrated sale (metric) really does allow you to make cuts that are accurate to the millimeter!