The USB board is nice, because in addition to having a built-in 5V-to-3.3V regulator and indicator LEDs, it’s got all the pins of the XBee broken out on the side of the board. Makes development of XBee projects easier.
The breakout board also has its own regulator on board, making it easy to interface with a 5V project. It’s also got the serial pins broken out to a single row, making it easy to mount on the side of a breadboard.
The prices on both are reasonable for the European market. As the US dollar continues to sink, they’re a bit pricier for US customers, but still reasonable, for now.
Thanks to Rob Faludi and Jeff LeBlanc for testing help, and to Luigi Carnevale for supplying sample boards.