PS if you do go the Wixel route, they are quite intelligent. If you configure them both in what they call serial_mode 0, they work correctly according to the way they are powered. So the PC one, which is powered by the usb port, automatically operates in usb to radio mode. The Arduino one, powered through the Wixel's Vin pin, automatically operates in its uart to radio mode. (Although you can over-ride that by explicitly setting a serial_mode other than 0; I have never needed to do that.)
There's also a downloadable configuration utility, to set eg that serial_mode. Great manual too.
Just a tad expensive I think, as I said.