This USB to serial adapter is compatible with ALL our Arduino Form Factor products. It is similar to other Arduino USB serial connections. It is required to program those boards, once programmed it may be disconnected and power applied other ways to the board.
For BASIC or C on BASIC many of the much cheaper boards you find on eBay are fine.
If you want to do bare metal C development with our tools or FlashMagic or need to update BASIC firmware, this board supports ISP programming without moving jumpers.
The serial interface chip is from FTDI.
The original board shown has a USB mini-B connector or we can supply them with micro-B connectors (same connector as a cellphone).