Yes, the Logitech USB dongle is radio.
I've been using wireless mice for years, not even Logitech and Apple can get Bluetooth to work consistently, pretty sad. As for 2.4, Logitech seems to rule that and has it pretty much perfected, others, not so much. It's bad enough to drop $100 on a mouse and have a bad experience, not sure I'd trust anyone else with an even more expensive keyboard.
Why use a wireless keyboard anyhow?
You still need to connect a cord to charge it and since it never moves (unless it travels, which still needs to charge occasionally) the cord's not really a big deal anyhow. Worse still, most wireless keyboards border on the limits of what is considered ergonomic (front row height), meaning they're absolutely TERRIBLE for your wrists unless you use a wrest which means even more stuff cluttering your desk (and/or needing to be carried when it travels).
More important, you watch what the mouse is doing because it uses hand eye coordination, you are not always watching what the keyboard does. You can lose a few steps on a mouse, especially in an office environment and probably not even notice but imagine losing random keystrokes or disconnecting entirely mid way through a paragraph before you notice. It's not a pleasant experience.
BTW
Logitech is now making MX based keyboards (with hot swap), cross your fingers for a wireless one soon, that would be my recommendation if it ever comes out, just remember batteries die. Usually about mid way through something important.
Also, in regards to the last poster's advice, do NOT get an aluminum wireless keyboard, that will only make the signal/connection problems worse.