I'd steer clear of them...
As for the chip... There is no chip in a factory mustang.
The ECU is in the passenger side door. A Proper chip plugs into the service port on the factory ECU. The ECU controls the engine.
The whole point of the chip is to re-calibrate the car and in the case of an automatic the transmission as well to give you more power and driveability.
I'd look to your local SCT Dealer. http://www.sctflash.com
Contact them for more info and to find someone who can help you out. They'll be able to get you a setup for your vehicle.
With that being said, personally, I'd look into an SCT Flash Tuner. The X2 or X3 will work well, many places sell them. SCT offers a Pre-Programmed version which works out very well for stock or near stock vehicles and you can always have you vehicle custom dyno tuned later on.