I think you would usually get this one if you were going to stack it on a Revo. As a Neo6 it is the cheapest. Also, you can use the GPS without soldering or making cables (mag requires a little more work though). Just take 4 of the 6 pins out of the GPS cable and put in an OP connector (JST-SH 4 pin 1.0mm)
Be aware that the GPS needs to be powered by 5V standard receiver power (can take more volts, it is regulated on GPS board), but the mag must have 3.3v. If you want to use the mag you need to either steal power from the GPS voltage regulator with a soldered wire on the GPS board, or somehow supply 3.3v to the other GPS connector (using an external voltage regulator).
I have successfully connected the GPS regulated voltage (3.3v) to the mag power, with a wire on the GPS board, and leave the external mag power wire disconnected. I also left off the mag ground wire and rely on the GPS ground wire.
I seem to have better luck calibrating this mag than I do a V9 mag in that it seems to stay green more. Could be other reasons involved though.
IIRC the mag needs a fairly high current pulse at a low duty cycle.
This and other options (especially this Neo8 with mag for $22
http://www.ebay.com/itm/251997592219 ) are discussed in some FTT only threads.