WiFly Breakout vs WiFly Shield?

I am trying to figure out which WiFly module to purchase for a project I am working on.

From what I have been able to figure out, the main difference between these two modules is that the shield frees up the Arduino's UART so that you can use the serial port for something else. Am I reading this right? I am pretty new to Arduino so I'm still learning and don't know much of anything, like what a UART is.

I'm working with an Arduino Mega and I have some probes that a future addon to my project will be using. If I get the breakout board, will I be unable to add on the probes later on?

Also, are there any other differences between the two WiFly modules that are important?

Thanks

Please give links to both shields docs or schematics.

Hi,
The WiFly breakout board interfaces with 4 pins (Rx, Tx, Gnd, 3.3v) and communicates via the Arduino's UART.
the WiFly Shield uses more pins and communicates via the Arduino's SPI pins.

Each uses different libraries as a result. Programming model differs as well (one day soon they will merge).

Both end up at an RN-131/RN-171 chip.

There are of course other more minor differences but the above are the major items.

Cheers,